Home Secretary John Reid has been heckled during a speech about targeting potential Muslim extremists.
He was interrupted by activist Abu Izzadeen, who said he was "furious" about "state terrorism by British police".
In his speech, Mr Reid asked Muslim parents to keep a close eye on their children and act if they suspected they were being radicalised by extremists.
It was his first speech to a Muslim audience since becoming home secretary.
Also known as Omar or Trevor Brooks
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The protester, also known as Omar Brooks, denies being a member of the banned al-Ghurabaa group.
He accused the minister of being an "enemy" of Islam before he was led from the building by police and stewards.
Respect MP George Galloway, in an open letter to Mr Reid written on Wednesday afternoon, asked how such a "well-known extremist... was allowed within punching distance of the British home secretary".
A Home Office spokesman said that, while Mr Izzadeen was not invited to the meeting, it was "in the nature of an open community meeting... that some people who were not invited ended up attending.
"There was no question of the home secretary's safety being compromised at any time."
A second heckler, who also interrupted Mr Reid's speech, was ejected a few minutes after Mr Izzadeen.
During his time in Leytonstone, east London, which also involved a visit to a mosque, Mr Reid said community and religious leaders could play a key role in the fight against terrorism.
The home secretary said "our fight is not with Muslims generally".
Instead, he said, there was a "struggle against extremism".
And, warning that terrorist fanatics sought to influence youngsters, he said: "There is no nice way of saying this.
"These fanatics are looking to groom and brainwash children, including your children, for suicide bombings, grooming them to kill themselves in order to murder others."
Following the speech, Metropolitan Police Commissioner Sir Ian Blair said it was "extraordinarily difficult" to clamp down on Islamic extremism without offending large groups of Muslims.
Speaking on BBC Radio Five Live's Simon Mayo programme, he said: "I have seen the incident, I think it isn't at all pleasant.
"But at the moment no law has been broken by that protester, and I think one of the most difficult jobs the police have is this line between free speech and abuse."
Mr Reid later described the hecklers as "unrepresentative" of the Muslim
John Reid asked Muslim parents to keep a close eye on their children
Speaking on Channel 4 News, he added: "If they are trying to shout me down, imagine what they are doing
to the vast majority of Muslims in their community."
But Massoud Shadjareh, who chairs the Islamic Human Rights Commission, said Mr Reid's demands were "unrealistic and not demanded from any other community".
He said he government, whose policies he said played a "substantial role" in radicalising people, "needs to come out of this state of denial, stop pointing fingers at others and instead recognise the root causes and its own responsibility".
Shadow attorney general Dominic Grieve said the home secretary should realise Muslim extremism was not a problem just for the Muslim community, but "for all of us".
The speech came weeks after some Muslim leaders expressed concerns about the UK's foreign policy and called for it to be changed, in a letter which Mr Reid then called a "dreadful misjudgement".