The Madrid bombings have prompted a huge influx of messages to BBC News Online.
The trains were packed when the bombs went off
We received 400 e-mails in the first two hours after the bombings, many from Madrid. By Friday evening, we had received well over 6,500 messages.
Many of them were sent by eyewitnesses of the attacks, or relatives of those caught up in them, and reaction from further afield.
Below are a selection of your comments:
It was 0740 [0640GMT] when the train from Getafe arrived at Atocha train station. As the doors opened, the first bomb exploded in a different train and platform. The train I was in, which I guess was some 50-75m from the bomb, was shaken. People got off quickly but still I feel we all kept calm. It was only one minute later that two more bombs exploded in rapid succession. It was at this point that people rushed out of the station. People crying. It was a shocking image. To be honest, I didn't stay any longer to see what happened.
Francisco Torres, Madrid, Spain
My mother was in one of those trains and the bomb exploded barely 20m far away of her seat. She wasn't injured but the man in front of her seat was dead. All the lights of the train went out. Everybody screamed and ran. Everybody is still phoning his/her friends and relatives to know if they are OK. All the people in those trains were workers and students. What will Eta [if they were responsible, because they usually warn before an attack and today there weren't any warnings] achieve with all these deaths? I think violence doesn't achieve anything, only shedding innocent blood and tears.
Alba, Alcala de Henares, Spain
The explosion in the train near Atocha Station [the second one] woke me up. The house where I live is next to the rail. My bed and all the building moved and a huge sound was heard. Then, I turned on the TV and the radio to try to find out what was happening. A burnt-plastic smell and an opaque cloud entered in my house when I opened the window, which is at the other side of the building. I committed the big error to go down to the street and I saw a train with six wagons and three big holes. People walking down the rails and others lying down on the ground. Pieces of the train in the street and dead people trapped in the twisted irons.
Fernando, Madrid, Spain
I was woken up by two strong blasts to the windows in our flat. It was like very strong wind - but I knew it wasn't wind. Ten minutes later there was another blast followed by sounds of sirens.
Duncan Briffett, Madrid, Spain
MESSAGES OF SYMPATHY
I haven't stopped crying all day. I keep seeing those images on TV and I try to find a reason why. There's no reason. Life is unfair, and the world has gone mad. When will we stop all this hate there's in this world?
Marc Granja, Barcelona, Spain
Does it really matter who it was? The people who definitely matter are dead. This is the day Spain cried out all our tears.
Gabriel Guillén, Alicante, Spain
Thank you very much to all the people around the world who are sending us their condolences and support. This is not an attack against Madrid; it's an attack against humanity. Today, everybody, everywhere, is a citizen from Madrid.
Rafael de la Ossa, Madrid, Spain
In this moment of sadness I just remember the words of Winston Churchill: We shall go on till the end, we shall fight them on the seas and oceans, we shall defend our island, whatever the cost may be, we shall never surrender.
Jose, Barcelona, Spain
DEALING WITH TERROR
Eta or not, this disgusting act of terrorism exposes a most serious threat. It is fairly obvious that explosions took place high in the carriages most likely from bags in the luggage racks. How do we prevent this, without mass screening of train passengers?
John Mason, Falkirk, Scotland
I live in Andalucia but we all are in shock (as I am sure the whole country is). I know this kind of terrorism from London and I know the son of an Eta victim (shot at point blank range). The public are led to believe that the terrorists never gain from their acts of terror and show their disgust so why continue? I think that the majority of acts now are committed by the new generation of the "political" terrorist groups who are motivated by their blood lust and have forgotten or never knew the initial motives of the founders of such groups. It is now an excuse to commit crimes and be praised by those around them.
Siobhean Gribbin, Estepona, Spain
There is no excuse for terror, no matter who when and why. There should be no other names for terrorists. Not freedom fighters, not militants, not separatists. Just terrorists. Our hearts are with the people of Spain.
Vladimir Beker, Israel
WHO DID IT?
11 September and 11 March and co-ordinated ruthlessness indicate for me al-Qaeda.
Thorbjorn Collin, Vasteras, Sweden
This is not the first terrorist attack that I have lived through in Madrid, but it is certainly the largest and, I hope, the last. There were roadblocks on the way to work yesterday, so I think the Guardia Civil suspected terrorist activity. This is definitely the work of Eta.
Simon Taylor, Madrid, Spain
A terrible and appalling tragedy - I can only imagine the terrible suffering of these people. Spain is a fantastic country and Madrid a fantastic city. My heart goes out to anyone affected by this disaster. As for identifying the killers, from a distant perspective I would urge caution in pointing the finger of blame. This atrocity may prove to be the work of extremist Eta activists and yet the scale is wholly unprecedented. How could this serve the Basque cause? Whoever was responsible, will I hope be caught and brought to account.
Neil Walker, Gloucester, UK
Arabic terrorists? No way! Why would they attack the general population of Spain - most of whom opposed the war in Iraq - instead of official targets? And just before election time, too - how convenient. Consider the detonators and a tape of the Koran found in a van and ask yourself: is this credible? Do terrorists - does ANY terrorist group - go around planting evidence against themselves? It's a frame-up.
Tom Kennedy, Montpellier, France
REACTION FROM AROUND THE WORLD
As a resident of Istanbul and a Turkish citizen my heart goes out to the victims of this cowardly terrorist act. Only three months ago, I also had to wake up with the sounds of explosions, and realise that my city was not that safe anymore. As the recent terrorist bombings in Istanbul and Madrid clearly demonstrate, there should never be any sympathy for people who use terrorism to correct the injustices suffered by others.
Kaan Sahilyol, Istanbul, Turkey
Madrid and all of Spain is known to all for it's warm-hearted, vivacious, and artistic people. My heart goes out to all, especially those who have lost close loved ones from this horrific act. From someone who was at the WTC [World Trade Center] on 9/11, stand tall. The whole world is by your side.
Mark Lutnes, New York City, USA
I'm speechless, and numb. I sympathise and offer all my warmest condolences to the Spanish people for this tragedy, and the loss of lives. I was shocked when I saw the pictures on TV and the death toll climbing and I just pray for the loved ones to deal with their pain and sadness.
Fatima, Oran, Algeria
My sincere condolences to all Spanish people... I try to understand but I cannot! Why all this hate? Why people killing each other? Not just in Spain... but all over the world.
Eder Matsumoto, Yokohama, Japan
Another Bali is an appalling thing. Our condolences to those who are now suffering from the evil act by amoral people - the end never justifies the means. Our prayers are with you.
Evan, Sydney, Australia