British police arrested two men and a woman today in connection with the attacks on the United States last week.
They were arrested in connection with the World Trade Center terrorist attack and are being questioned by Anti-Terrorist Branch officers, a Scotland Yard statement said.
A man of 27 and a woman of 25 were arrested at a house in west London this morning. A 29-year-old man was arrested later in the city of Birmingham, and was also taken to London for questioning, police said.
Metropolitan Police Commissioner Mr John Stevens said today that London was on the highest peacetime security alert in its history, with 1,500 extra officers on the streets this weekend.
London is at risk because it is one of the world's major capital cities, although there has been no specific threat, he said. Britain has vowed to hunt down anyone associated with last week's devastating attacks on US landmarks who may be living in Britain.
Minister for Europe Mr Peter Hain said intelligence was being shared with US investigators seeking those responsible for the suicide hijackings that killed thousands in New York, Washington and Pennsylvania.
The Daily Mail newspaper reported on Tuesday that five of the hijackers had trained in Britain, and that the FBI had passed names and details to British police.