Police should come down "heavily" on anti-cartoon protesters who broke the law, a Cabinet Minister demanded today as an extremist cleric called for the artist to face execution.
The Northern Ireland Secretary Peter Hain said the actions of some Muslims in London at the weekend had been "completely unacceptable and intolerable".
Placards threatened a repeat of the 11 September and 7 July atrocities following the publication of cartoons in Denmark depicting the prophet Mohammed, sparking calls for action.
Amid violence in cities across the world - which has seen one death in Afghanistan and embassies torched - UK-based Muslim groups condemned extreme aspects of the demonstrations here.
But radical cleric Omar Bakri Mohammed insisted on the BBC this morning that anyone who "insults a prophet" must be punished and executed.
That did not mean a vigilante murder, he insisted, but warned that any country which refused to put people on trial for such insults would have to "face the consequences".
Reacting to the protests, Mr Hain said on the BBC Radio 4 Today programme: "Demonstrators on the streets over the weekend were doing things and saying things that are completely unacceptable and intolerable.
"The police need to bear down on them very heavily and chase down those who have committed offences and prosecute them where they can get the evidence, because there is freedom of speech on the one hand - that is sacrosanct.
"But on the other hand, incitement to terror, incitement to suicide bombing - all of those are clear infringements of the law.
"And where there is evidence to back that up, then prosecutions will obviously follow and the police are investigating that now."
The demonstration was condemned by a range of Muslim organisations, from the moderate Muslim Council of Britain to the more radical Hizb-ut-Tahrir, which Prime Minister Tony Blair is seeking to outlaw because of claims it backs terrorism.
Hizb-ut-Tahrir organised a less incendiary protest in London on Saturday, which passed off without incident.
The Shadow Home Secretary David Davis has called for a "no tolerance" approach from the police to banners whose slogans consisted of incitement to murder.
Specialist police officers who attended the demo were understood to have taken film and photographic evidence, but no protesters were arrested.
The Metropolitan Police spokeswoman has said any arrests would be made "at the appropriate time".
Lord Harris, a board member of the Metropolitan Police Authority, backed the policing of the demonstrations, saying immediate public safety had to be the first consideration.
"It is much more important to deal with that and to make sure that people in the immediate environment are physically safe and then to assess whether other offences have been committed.
"That, I think, seems to have been the approach in this case, but we will need to look at it in some detail."
Bakri Mohammed, who left the UK for Lebanon in August amid suggestions he might be charged with treason for allegedly praising the July 7 bombers, said on the programme: "The insult has been established now by everybody, Muslim and non-Muslim, and everybody condemns the cartoonist and condemns the cartoon.
"However, in Islam, God said, and the messenger Mohammed said, whoever insults a prophet, he must be punished and executed.
"This man should be put on trial and if it is proven to be executed."
Muslims around the world must not kill anyone who insulted Mohammed "by their own personal, individual initiative", he added.
"We are not saying ourselves to go there and start to look to him and kill him, we are not talking about that. We are talking about Islamic rules. If anybody insults the prophet, he will have to take a punishment."
One man who was pictured dressed up a suicide bomber at the protest has defended his actions and said he wanted to expose "double standards".
Building student Omar Khayam, 22, of Bedford, said: "I would do it again to make a point. I could have gone and held up banners or something, but this made the point better.
"If certain people have the right to do what they want and other people don't, then that is double standards."
* Hundreds of Afghans clashed with police and soldiers today during a demonstration against the publication of cartoons of the Prophet Muhammad. One person was killed and four were wounded. Police fired on the demonstrators after a man in the crowd shot at them and others threw stones and knives during the rally in the central Afghan city of Mihtarlam, said a spokesman for the Interior Ministry.
* Riot police in New Delhi fired tear gas and water cannons to disperse hundreds of students protesting against the publication of cartoons of the Prophet Muhammad in European newspapers. The protesters chanted slogans and burned a Danish flag before riot police broke up the demonstration.