Two men were seriously hurt when they were stabbed in clashes between the English Defence League and Muslim protesters after a 9/11 memorial service in London.
The two men are thought to have been on opposing sides during a pitched battle outside a pub in Edgware Road last night.
The groups staged rival protests outside the American Embassy in Grosvenor Square during a minute's silence to mark the moment when the first hijacked plane hit New York's World Trade Center 10 years ago.
About 100 activists from radical Islamist groups including Muslims Against Crusades set fire to a US flag while others shouted slogans including "USA terrorists".
Sixty members of the far-Right group staged a counter demonstration and both groups then took part in an unplanned 90-minute march along Park Lane and Edgware Road to Regent's Park Mosque.
A fight broke out outside the Tyburn pub in Edgware Road in which the two men were stabbed. More than 40 people were arrested during the day, 13 of them in connection with assaults during the brawl at about 6pm.
An eyewitness, who did not wish to be named, said: "There was a group of EDL guys drinking outside the pub when a large group of Muslims walked past. The EDL started hurling racist abuse at the Muslims who took offence. They got angry and were yelling back. Then the EDL guys picked up pub furniture and started throwing glasses and chairs and tables at the group in the street.
"It was chaos. At first it was just 10 EDL guys but that number quickly swelled to about 50 people. The police were on the scene really quickly. They separated the groups and just started arresting people."
Earlier radical Islamists, including hate preacher Anjem Choudary, gathered in Grosvenor Square as families of British 9/11 victims prepared for a remembrance ceremony in the September 11 memorial garden.
A smaller group of Muslims staged a counter-demonstration nearby, holding up placards reading "Muslims Against Extremism" and "If You Want Sharia, Move To Saudi".
London Evening Standard