A Home Office minister has urged people not to over-react to the video testament of a London suicide bomber.
In the tape, Mohammad Sidique Khan accused Western governments of atrocities against Muslims.
Baroness Scotland said Khan was blaming the Iraq war for his actions but she did not believe it was responsible as there were attacks before the conflict.
The Conservatives say the tape will sicken people and the Lib Dems say there can be no excuse for extremism.
The tape shows Khan in a broad Yorkshire accent saying: "Until we feel security, you will be our targets. And until you stop the bombing, gassing, imprisonment and torture of my people we will not stop this fight."
In a second message on the same tape, al-Qaeda deputy leader Ayman al-Zawahri said the Tube attacks were a "slap" to the policies of Tony Blair.
Appeal for caution
Downing Street and the Foreign Office have not so far commented on the tape.
But Baroness Scotland told BBC Radio 4's Today programme: "I know he says that what happened in Iraq is responsible for these actions but I don't think it is.
"It is a terrorist act and we have to be really cautious about how to respond."
The Home Office minister said it might have been Khan's perception that the Iraq war was a motivating factor but terrorists had struck in Africa and across the world before the war.
"It's one of the most dreadful things that people have distorted issues for justification for acts of terrorism," she said.
Asked whether it raised fears of further attacks, Baroness Scotland added: "We are constantly vigilant. That is absolutely going to continue."
Labour MP Shahid Malik said there had been a "degree of complacency" since the July bombings in London.
The tape was a chilling reminder of the need to be watchful and explained why ministers had been "upping the ante" against those posing a threat, he said.
The Dewsbury MP said the tape also put pay to those British Muslims who were "in denial" about the identity of the bombers and who had spread conspiracy theories.
"There is a hardcore rump within the British Muslims community that didn't actually believe that Sidique and his twisted associates were responsible for the seventh of July, he said.
Mr Malik called the video "utterly grotesque" for suggesting Westerners were somehow responsible for the bombings when the bombers were the only people to blame.
But for the first time it gave an insight into the mind of a suicide bomber - "the enemy within".
"I think that people might well have sympathy with some of the causes that Sidique professes to support.
"The fact is that defending just causes with evil acts serves only to malign those causes."
Conservative shadow home secretary David Davis said: "People across Britain will be sickened by this video. Nothing can justify the murder of innocent people".
Liberal Democrat home affairs spokesman Mark Oaten said there could be no justification for the bombings.
"Britain's involvement in the war in Iraq is no excuse for Muslim extremism," he said.
"However, it would be wrong for the government to deny that Muslim communities feel a sense of unease about our involvement in Iraq."
Former Tory Foreign Secretary Sir Malcolm Rifkind said there was a widespread belief in the Muslim community that UK foreign policy was anti-Muslim.
Such claims were wrong, he said, urging ministers to work harder to explain foreign policy and highlight help for Muslims in episodes such as the Kosovo war.