Members of the English Defence League protest against a march by Muslims Against Crusades outside the American Embassy in London

Around 40 people were arrested by police following disorder sparked by protests that marred the 10th anniversary of the 9/11 terror attacks, police said.

Members of the group Muslims Against Crusades burn the American flag during a protest outside the American Embassy in London

A crowd of 100 activists from radical Islamic groups including Muslims Against Crusades (MAC) congregated outside the US Embassy in Grosvenor Square yesterday, while members of the English Defence League (EDL) staged a counter-demonstration.

Trouble later flared between the two groups and two men were stabbed outside a pub in an incident believed to be connected to the protests.

The radical Islamic supporters gathered in the central London square as families of British 9/11 victims prepared for a remembrance ceremony in the September 11 memorial garden.

Protesters set fire to a US flag during a minutes silence held to mark the moment when the first hijacked plane hit the World Trade Center, while others shouted slogans including USA terrorists and brandished anti-American placards.

After two hours the MAC demonstration left the area, shortly before the start of the memorial service.

But that resulted in chaotic scenes in central London as Islamic protesters and EDL supporters participated in an unplanned 90-minute march along Park Lane and Edgware Road to Regents Park Mosque.

On several occasions police were forced to intervene to keep the two groups apart, while traffic was brought to a standstill.

A Met Police spokesman said: Four people were arrested during the afternoon for alleged public order offences and were taken to south London police stations.

The (Islamic) demonstrators were subsequently escorted by police to the Central London Mosque. A number - believed to be four or five of this group - were arrested during this journey.

He added that around 20 demonstrators opposed to the Islamic groups were arrested for breach of the peace in the Oxford Street area.

Meanwhile, police said 11 people were arrested outside The Tyburn pub on Edgware Road, near Marble Arch, after two men were stabbed.

The force spokesman said the men, who are both believed to be opponents of the Islamic groups, were injured in the incident at 6pm, over two hours after the main protests had ended.

The condition of the two victims is unknown but the spokesman said they remained conscious following the incident.

One of the Grosvenor Square memorial service attendees, who did not want to be named, said the protesters should have been stopped from standing just across the road from the embassy and using a loud speaker system.

The man, whose cousin died in the terror attacks, said: They shouldnt be allowed to do it. Its very disrespectful. Its too loud.

He added: They can say what they want but not with the loudspeaker. They shouldnt obstruct the service.

Tom Clarke, who lost his sister Suria, a 30-year-old PR executive, in the attacks on the World Trade Center, said he would have preferred it if the protesters had not staged the demonstration.

But he added: I would much rather live in a country where people are allowed to do that than one where they arent.

I would defend their right to protest and have the right to say what they want.

A small group of Muslims staged a demonstration opposing the radicals, holding up placards reading Muslims Against Extremism and If You Want Sharia, Move To Saudi.

Abdul Sallam, 41, travelled down to London from his home in Glasgow to show the strength of his feelings.

He said: Im a Muslim. What theyre doing is bringing shame on all Muslims.

This is not part of the teachings of Islam.

Islam is all about peace, but what they want to do is hate other people.