Thursday's bomb attacks in London have left scores of people dead and hundreds injured, some critically.
Security analysts say the blasts bear the hallmarks of al-Qaeda. A statement on an Islamist website - purportedly from al-Qaeda - has claimed it was behind the attacks.
Readers from the BBC's language sites have been discussing what the attacks mean for the global war on terror, whether further attacks can be prevented and whether anti-terror laws have proved ineffective.
"I blame the so-called 'war on terror' for this attack"
Matt, NYC, USA
"We should look at the reasons why they did this"
Abdolvahab, Mashhad, Iran
"The London bombings are like daily events in Iraq"
M Abu Kalal, Najaf, Iraq
"We need to finish the root causes of terrorist activities"
Yaseen, Sialkot, Pakistan
"Al-Qaeda are very much alive and kicking"
Ashutosh Balwaria, India
"It's necessary to destroy all the sources of financing of terrorism"
"It is time to adopt more drastic measures"
Lucia, Jalisco, Mexico
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There is almost nothing Londoners can do to prevent such attacks except to be more vigilant. The anti-terror laws have done little except limit our liberties. It is really a problem to do with international politics, i.e. a powerful extremist ideology that feeds off discontent in Islamic lands. The so called 'war on terror' has if anything fuelled terrorism and this attack is almost wholly due to our invasion of Iraq.
James Wild, London, UK
The UK beat terrorism once in the form of the IRA and can do it again. The way to beat terrorism is by destroying the ideology not the terrorist as in Northern Ireland. A terrorist is easily created if there is an ideology for him to follow. An ideology of hate is not so easy to create if people feel that there is social justice democracy and accountability. Blair should realise that Bush's 'war on terror' is a big failure.
Vajid Ali, Birmingham, UK
It is unfortunate it has taken an incident of this nature to unite the G8 heads. Furthermore, Bush is now able to drive focus towards the war on terror and in doing so can dim the limelight on his stance on Africa and global warming. I truly hope that this attack will not encourage more pro-war feelings, which will only increase the gap between the West and Middle East and jeopardise the safety of innocents on both sides.
Jacs, Austin, Texas, USA
Even we in the Middle East aren't immune to terrorism, as the bombing in Doha a few months back has shown. The only way to stop these people, in my opinion, is to show them how little support and popularity they have amongst their own people. Perhaps they will feel remorse as a result.
Sufyan, Doha, Qatar
I blame the so-called war on terror for this frightening attack. Joining the US in Bush's unrelated and unprovoked attack on Iraq has made London a target, nothing else. Bush and Blair have made the world more dangerous for all of us.
Matt, NYC, USA
Since the attack on Afghanistan, the US has not been serious in fighting al-Qaeda, because it sees al-Qaeda's existence necessary for the American forces to remain in Afghanistan. As long as the US just talks about fighting the terrorism (rather than taking action), we cannot be immune for terror attacks, be it in Madrid or Tehran or London or Baghdad. We should really think about where the next target would be.
Hamed, London, UK
Killing defenceless people is condemned from a religious and humanitarian point of views. Those who kill people in the name of religion do not really believe in the religion in their hearts. I sympathise with the victims from the bottom of my heart.
Ali Salemi, Tehran, Iran
Of course any terrorist act against innocent people in condemned, but we should look at the reasons why they did this in an impartial way. Why did this group (al-Qaeda) start their activity in London? We should not forget that no criminal would commit crimes without any reasons and there are factors that would provoke them to do that.
Abdolvahab, Mashhad, Iran
I think these bombings are the work of al-Qaeda; it could be because of Britain's actions in Iraq and its co-operation with the US in occupying Iraq. The people of Iraq, or any other country, are so sensitive about the occupation of their country. Since Iraq is an Islamic country, al-Qaeda has attacked Britain.
Shahram, Kerman, Iran
The killing of innocent humans is done by a small group of ignorant people. Their crimes have now reached Europe as well. But this not the end of it. Groups of this kind are doomed.
Ramin, Ahwaz, Iran
The ghastly explosions in London are a sign of a bigger threat against the whole world. I condemn these attacks and just want to say that reforming extremist governments from within, is not possible due to their repressive nature.
Shahram, Tabriz, Iran
The roots of terror in the world are actually the people who do not think logically. They do not have any relationship whatsoever with true Islam. With these acts, they only show how far they are from being human. I hope real democracy will prevail in the whole world and people in every country can have their fate in their own hands without the interference of other countries.
Mohammad, Qom, Iran
America is responsible for what is happening. They are the ones who created Bin Laden.
Majd, Qalqiliya, Palestinian territories
I read the statement of the group that claimed responsibility of this cowardly act. They understand nothing about Islam. If they were men let them get out of their hideouts - women and children killers are nothing but criminals and cowards.
Abu Zeinah, Lebanon
It is really a catastrophe if they think that by their acts they are defending Islam. My condolences to the British people.
Mohamed Ghandour, Egypt
A cowardly act of terror that killed women and children. The criminals are not humans and have no feelings, they are but criminals and killers and they are not Muslims and do not represent Islam in any way.
Abu Azeez, Denmark
It is a terrorist act intended to create chaos and kill innocents everywhere. The same thing is happening in Iraq, where the terrorists are targeting women and children. We condemn this criminal act. Let those who support the terrorists know that the people they are supporting are criminals who have no principles.
Sakar, Kirkuk, Iraq
It is a disgusting act that brings to memory the 9/11 atrocities and the Madrid bombings. Al-Qaeda terrorists are still operating; more work is needed to eliminate them. The London bombings are just like the daily events happening in Iraq and it is always civilians who are the victims.
Mohamed Abu Kalal, Najaf, Iraq
We have to bring to justice those cowards who have committed these atrocities. The law must punish those who have sheltered and helped them to carry out their dirty mission. We pray for the victims, and our best wishes for the injured and their families.
Abu Ahmad, Iraqi in UK
Implementing one's thoughts by force is not to be encouraged I can't support such groups and this is ridiculous. These blasts remind me of the daisy cutter bombs thrown in Afghanistan and Iraq by the UK and USA, although the London blasts were barely one percent of the destruction in these said countries.
Sohail Niazi, Peshawar, Pakistan
First of all I fully condemn these attacks. This is a big violation of human rights. We should be alert to such attacks in future. There is a need to finish the root causes of such terrorist activities.
Yaseen, Sialkot, Pakistan
We should try and find out who is responsible as soon as possible so that such tragedies and acts of terrorism can be prevented in the future.
Shahid Butt, Lahore, Pakistan
Wherever such attacks happen, they should be condemned. However what I cannot understand is how can people be so sure that 'Muslims' are responsible for these attacks, when the investigation is still ongoing?
Nasi Chaudhry, Tokyo, Japan
These attacks have probably made the West realise the pain of seeing your loved ones covered in blood. This is what happens every day in Iraq and Afghanistan.
Sarfaraz, Mumbai, India
The UK needs to improve its security system. It's sad that these attacks happened in spite of such well trained security forces.
Farhan Khan, UK
This is a cowardly act. The terrorists and their supporters want to terrify innocent people and disturb the economy. I don't think they will be successful. They will be destroyed if we destroy them and their supporters.
Prem Raj, Michigan, US
It's not good but it's happening all over the world due to the bad policies of America and Britain. Every action has a reaction, so whole of the world should try to stop such acts.
Junaid, Muscat, Oman
This was al-Qaeda's statement that they are very much alive and kicking. They are capable of doing the same thing as they were before Bush invaded Afghanistan, Iraq, spent a fortune of money and sacrificed thousands of lives of his soldiers. It's a slap in the face for people who think that Bush and Blair have succeeded in cutting the legs off al-Qaeda.
Ashutosh Balwaria, India
The war against terrorism has not been able to cause much of a dent. How do the governments propose to protect the innocent and vulnerable people from it? Only yesterday London had first hand experience of a calculated terrorist attack and joined other trouble spots across the world who have been bleeding from it. Whatever be the cost to the community, terrorists should not be allowed to hold any part of this world to the ransom.
Peter Parkash, NSW, Australia
Killing innocent people is heinous crime which has to be deplored in strongest terms. The perpetrators of such crimes have no religion. Their only intention is to spread fear and impose their culture of death on a civilised world. It is useless to blame the US or its allies for every terrorist attack. Firm unity has to be shown to combat such menace otherwise, tomorrow, it may be one of your cities.
Prem Xalxo, Rome, Italy
My deepest condolences to all those directly or indirectly affected. I think in these days there's no place for any wise thoughts or profuse talk. We are unable to comprehend everything that is going on.
Terrorism is like a hydra, we have to know this environment thoroughly and try to minimise it relentlessly. There's probably a need to apply a great effort, financial spending, monitoring, technologies - all to keep this phenomenon under control. The most important thing is for terrorism not to be an organised thing. Its total extinction is possible only with the priority of human life being set as a norm.
My condolences to the victims. I condemn what happened. We need to shift to common standards of fighting the terrorist threat. No local measures will improve the situation, there's no way of getting a policeman to each single terrorist. We need to understand - terrorism is not somewhere far away, in Iraq, Afghanistan, Chechnya... it's all around us. It's useless to fight it only with force. The alternative is economical, cultural and educational measures in close co-operation with internal politics.
Valery, St Petersburg, Russia
No matter how many victims there are from terrorist acts in Britain, the West will never understand the pain and the feelings of terrorists victims in Russia.
Andrey K, Russia
It's sad, very sad and painful to see the humanity sinking deeper and deeper into this abyss of violence. And the worst thing is I don't know who to believe. Yes, it's all awful - the death of innocent citizens. But in recent years we're witnessing how easy it is to manipulate the public opinion, without which governments of certain countries find it difficult to achieve their goals. I am a Muslim and I affirm that no Muslim will ever spill the blood of innocent people. If this was done by people calling themselves Muslims and in the name of Islam, than this terrorist attack clearly damages the image of Islam. Great Britain has always been a refuge for millions of Muslims and has always distinguished itself as a liberal country.
I sympathise with you - terrorism is a worldwide evil. Everyone has to fight it. It's necessary to destroy all the sources of financing of terrorism and to find out who benefits from it and who benefits from such death.
The unfair and unexpected death of any person has to be condemned, especially the deaths of those who are innocent. I am really sorry for London, a city where I had very happy moments and where my sons have learnt what it means to live quietly.
Freddy Carrillo, Caracas, Venezuela
Two years ago my father was killed by a car bomb, along with 30 other people and many more injured. Sincerely I believe that there is nothing to be done. The human being has the natural capability to forget and probably that is why a society can survive when something like this happens. My mind and heart are with the families affected in this incident.
Laura Maria Jimenez, Bogota, Colombia
I believe the only way to deal with terrorism and other problems like gangs or drug trafficking, is strengthening the rule of law. Today it seems that there is a battle against radical and extremist Islam groups, who claimed that their commit this acts because of the invasions of Afghanistan and Iraq. It is a never ending story. Until these groups feel the strength of the law, many things will change.
Jony Cifuentes, Guatemala City, Guatemala
The US and UK have killed thousands of innocent people in Iraq and Afghanistan. I do not see condolences for grieving Afghan families neither see the Pope condemning this incident. Is the life of a British woman or child more worthy than an Afghan one? Death is painful, wherever it strikes, but whoever kills innocents cannot expect anything good.
Jose Castillo, Caracas, Venezuela
From my point of view it is totally unacceptable that more innocent people continue to die in this way. It is clear that UK security measures are not working and will not work. It is time to adopt more drastic measures against these people without soul. It is not easy but how long are we going to suffer in these situations? It is time the powerful countries do something now.
Lucia, Lagos de Moreno, Jalisco, Mexico