Tony Blair has called for tougher laws and a global drive to tackle the "evil" ideology behind the London bombings.
The investigations are moving at a speedy pace
Mr Blair said there would be "profound shock and anxiety" after the news the suspected suicide bombers were British.
Talks are to begin on bringing in new laws covering preparations for attacks and to make it easier to deport people trying to "incite hatred", he told MPs.
Mr Blair, who is to host a summit of UK Muslim leaders, said the "moderate and true voice of Islam" must be mobilised.
Police seeking the masterminds behind the attacks are believed to be looking for a fifth person in connection with the attacks which killed at least 52 people in London last Thursday.
The uncle of one of the suspected London suicide bombers said his family had been "left shattered" by the news.
Bashir Ahmed, 65, said the family of Shehzad Tanweer, who recently studied religion in Pakistan, could not accept he was capable of the bombings.
BLAIR'S FOUR-POINT PLAN
New laws as planned against incitement and instigation of terrorism
New measures to keep people inciting hatred out of the UK, or making it more easily to deport them
Help for the Muslim community to counter the "evil" interpretation of their faith
International effort to mobilise the "moderate and true voice of Islam"
In Parliament, Mr Blair said there was "a need and a willingness to act".
Consultations would begin in the next couple of weeks over possible new anti-terror legislation, due to be published this autumn, he said.
The laws would focus on measures the police and security services believed necessary to "combat the incitement and the instigation of terrorism as well as the acts of terrorism themselves".
"We will look urgently at how we strengthen the procedures to exclude people from entering the UK who may incite hatred or act contrary to the public good and at how we deport such people if they come here more easily," he continued.
Mr Blair said security measures alone would not deal with what was more than an isolated criminal act.
"It is an extreme and evil ideology whose roots lie in a perverted and poisonous misinterpretation of the religion of Islam," he said.
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Mr Blair met Muslim MPs on Wednesday morning to discuss how to tackle "this evil within the Muslim community".
"In the end, this can only be taken on and defeated by the community itself," he said.
The prime minister condemned any attacks on British Muslims, saying the vast majority were decent and law abiding.
There had to be international efforts to mobilise the true Muslim faith, he said.
Conservative leader Michael Howard said anyone who nurtured resentment against Muslims would be behaving in the way terrorists wanted.
He said: "It will take us a long time to come to terms with the fact that these attacks appear to have been committed by those who were born and brought up in our midst."
Liberal Democrat leader Charles Kennedy said everyone shared "a sense of national dismay" on hearing the bombers were British.
Everybody should keep stressing that the vast majority of Muslims totally condemned the bombings, he said.
Labour's Shahid Malik, whose Dewsbury constituency was the scene of police raids in the bombing investigation, said the Muslim community faced a "massive wake-up call".
Mr Malik added: "The challenge is straightforward - that those voices that we have tolerated will no longer be tolerated."
Liberal Democrat MEP Baroness Nicholson has suggested the bombings amounted to a "civil war", prompting criticism from Tory MEPs.
But she said her words should not be taken out of context and were "merely to point out the fact that last Thursday British citizens attacked other British citizens and nothing more".
The UK Home Office also denied the suggestion by French interior minister Nicolas Sarkozy that some of the suspected London bombers had been arrested in 2004.