Around 50 demonstrators brandished anti-US banners, chanted slogans and burnt a small piece of paper with a picture of the US flag on it outside the US embassy ni London, an AFP journalist at the scene said.
Britain's Press Association news agency reported that the protesters were from a group called Muslims Against Crusades.
They were seeking to disrupt a moment's silence observed to mark the moment when the first hijacked airliner hit the World Trade Center in New York 10 years ago, starting the attacks.
When they began burning the paper outside the embassy in central London, police formed a line near them but there was no violence, according to the AFP journalist. The small blaze went out in about a minute, he said.