Tony Blair has warned that terrorism continues to be a "global" threat and needs to be fought whether it is in "Iraq, Afghanistan or anywhere else".
He said his view was "not popular", but the "large part of the Western world" which blamed George Bush was wrong.
"This is a very deep-rooted problem right round the world... if we don't fight it it's going to come after us," the prime minister told the BBC.
He spoke before he and other ministers were briefed by the new head of MI5.
Jonathan Evans delivered his briefing at the first meeting of the new committee on security and terrorism, which brings together intelligence agency representatives, police and Whitehall officials and ministers.
It is intended to streamline the approach to security threats.
Speaking about terrorism on BBC Breakfast, Mr Blair said: "We have to fight it whether it's in Iraq or Afghanistan or anywhere else."
Mr Blair acknowledged the situation in Iraq was "hugely difficult".
"It's difficult because you have external elements - al-Qaeda up near Baghdad, and Iranian-backed elements down in Basra - who are deliberately creating the problem."
He said it was not true that Saddam Hussein "was a kind of lid" on sectarian violence which "poured out" once the dictator was toppled.
"If you talk to ordinary Iraqis - whether they are Sunni or Shia - they want to live together. You have these outside terrorists coming in and linking up with internal extremists and causing this carnage."
He also said it was wrong, as "a large part of the Western world" says to blame President Bush for terrorism.
International and domestic
Of the new ministerial committee, held for the first time on Tuesday, Mr Blair's spokesman said: "Today's meeting received an assessment of the current threat from the new director general of the security service (MI5) and agreed a programme to look at international terrorism and linkages to the UK, as well as the struggle for values and ideas.
"It's a recognition of the seriousness of the threat and that that threat is both international in character and also, for a very, very small minority, domestic in character."
The committee, expected to meet monthly, will be backed by a new Office for Security and Counter-terrorism (OSC), which will meet weekly and be chaired by the Home Secretary.
Part of the OSC's role is to provide a forum for the intelligence agencies to pass on information to the police and other relevant bodies.