Tony Blair has flown back to the UK from America amid growing debate over his policy in the Middle East.
In a speech before leaving he warned of an "arc of extremism" and said the West had not been "bold enough... in fighting for the values we believe in".
But his words were branded "foolish" and "naive" by former Foreign Secretary Sir Malcolm Rifkind.
And deputy UN Secretary General Mark Malloch Brown urged Mr Blair to take a back seat in Mid-East peace talks.
During his four day trip to America, Mr Blair held talks with US President George Bush, addressed top executives from Rupert Murdoch's News Corp and met Californian Governor Arnold Schwarzenegger.
But it was his speech on Tuesday to the World Affairs Council which has attracted the most headlines.
In it, Mr Blair said: "There is an arc of extremism now stretching across the Middle East and touching countries far outside that region."
And he called for a policy re-think, to deal with a war "of a completely unconventional kind".
"It is in part a struggle between what I will call reactionary Islam and moderate, mainstream Islam. But its implications go far wider.
"We are fighting a war, but not just against terrorism but about how the world should govern itself in the early 21st century, about global values," said Mr Blair.
"We... have to empower moderate, mainstream Islam to defeat reactionary Islam," he said.
He said it was not possible to say that this was being won, in the short term, adding that this was "because we are not being bold enough, consistent enough, thorough enough, in fighting for the values we believe in".
Mr Blair, speaking in Los Angeles, said Syria and Iran were miscalculating if they continued to support terrorism and said they would "be confronted".
During his trip Mr Blair has continued to avoid calling for an immediate ceasefire in Lebanon - instead sticking to the form of words that he wants an end to hostilities and a proper plan for longlasting peace.
The BBC has learned that Foreign Secretary Margaret Beckett had urged Mr Blair to press the US to call for an immediate end to hostilities - a call Downing Street rejected.
Reaction to Mr Blair's speech in the UK has been mixed.
Michael Moore, for the Liberal Democrats, said: "After the disastrous involvement in Iraq and the current crisis in the Middle East, the prime minister is on the wrong side of all the arguments.
"He may be signalling a major rethink in his approach, but it is hard to find real concessions in this speech."
Former Conservative Foreign Secretary Sir Malcolm Rifkind said it was "either naive or over-simplistic" of the prime minister to say conflicts such as those in Chechnya or Kashmir were part of a "world battle against terror".
"In Chechnya it's not a battle between freedom and terrorism, it's between Russian nationalism and Chechnya nationalism.
"In Kashmir, it's between India and Pakistan and to try and just draw all these threads in and simplify it in a rather foolish way indicates that the prime minister has become totally bereft of original thinking."
He added: "The single greatest triumph of what he (Mr Blair) calls Islamic terrorism has been in Iraq, which is a direct consequence of his own policy and that of George Bush."
Sir Malcolm was accused of "automatic pilot Blair-bashing" by former Labour minister Denis MacShane.
He said Mr Blair was making "a serious intellectual effort to try and think of foreign policy in a different way".
One of Tony Blair's former foreign office ministers, Tony Lloyd, said he hoped Mr Blair's speech represented a move away from US policy.
"I hope it's a rowing away from Washington," he told BBC Radio 4's Today programme.
Former minister Joan Ruddock said there was "despair" within the Labour ranks at Mr Blair's stance on Lebanon which, she warned, could spill over into the party conference in September.
"I have not met any member of the Labour Party myself who actually agrees with our strategy," she told BBC Radio 4's The World At One.
Merthyr Tydfil Labour MP Dai Havard has written to Mr Blair calling for an immediate ceasefire in Lebanon.
In a scathing attack on the prime minister, he accuses Mr Blair of being "deluded" if he thinks he has any influence over US President George Bush.
And he attacks Mr Blair's "misdirected obsession" with being a mouthpiece for the Bush administration.
Ann Clwyd, chairman of the Parliamentary Labour Party, said the "vast majority" of backbench Labour MPs wanted a ceasefire between Israel and Lebanon and were critical of Israeli policy.
The row comes as Kofi Annan's deputy at the United Nations urged Mr Blair to take a back seat in the negotiations to end the violence in the Middle East.
Mark Malloch Brown said the UK should be ready to be "a follower, not a leader" in the current crisis.
"It's not helpful for it again to appear to be the team that led on Iraq. This cannot be perceived as a US-UK deal with Israel," he told The Financial Times.