The Government is preparing to draw up further anti-terrorist legislation in the wake of a suspected al-Qaida plot to bomb a British target.
Prime Minister Tony Blair said he was prepared to bring forward measures to introduce identity cards.
The Muslim Council of Britain, meanwhile, said it had received an "overwhelmingly positive response" from the Islamic community after it reacted to news of the alleged plot by writing to 1,000 mosques urging them to guard against terrorists.
But the outspoken London-based group Al-Muhajiroun said Muslims should not co-operate with the authorities against other members of the faith.
Its leader, Sheikh Omar Bakri Muhammad, said: "Co-operating with the authorities against any other Muslims, that is an act of apostasy in Islam."
He also accused the UK and the United States of "terrorist activity" in Afghanistan and Iraq.
At his monthly Downing Street news conference, Mr Blair said: "I think we will need to readjust our terrorism laws still further.
"I think the whole issue of identity cards, which a few years ago were not on anyone's agenda, are very much on the political agenda here, probably more quickly than we anticipated."
He denied that the current anti-terrorism legislation was aimed at Muslims but said the police had to be prepared to take action against the terrorist threat.
"This particular form of terrorism is based on what I think the vast majority of Muslims would accept is a perversion of the true faith of Islam."
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