A former Guantanamo Bay detainee has told of how prison guards threw the Koran on the floor of his cell to make him fight them.
The protesters held Friday prayers in the street
Martin Mubanga, from Wembley, north London, was addressing more than 300 Islamic protesters outside the US Embassy in central London.
Demonstrators chanted the name of Osama bin Laden and burnt the American flag.
It follows a report by a US magazine about the desecration of the Koran at the centre, which was later retracted.
Speaking in Grosvenor Square on Friday Mr Mubanga said: "This is not something new. It is something old."
He said the detainees made it clear it was important that the Koran was never thrown on the floor and asked for notices to inform American soldiers of this.
"Time and time again new units, new soldiers would come and they would use the excuse that these new soldiers did not know how to handle issues around the Koran," he said.
Mr Mubanga was released in January after three years at the prison in Cuba.