British police are questioning four people in connection with terrorist attacks in the United States.
Anti-terrorist police are questioning three men and a woman at a high-security jail in central London.
Scotland Yard detectives arrested two men, aged 27 and 29, and a 25-year-old woman in separate raids on two houses in West London on Friday. A fourth man was arrested in the central British city of Birmingham and then brought to London.
These are the first arrests reported in Britain stemming from the suicide plane attacks on September 11 on the World Trade Center in New York and the Pentagon near Washington. The four can be held for up to seven days without charges under Britain's anti-terrorism law.
The arrests come as security remains high across London. About 1,500 extra policemen are on the streets.
London Police Commissioner John Stevens says Britain could be the next target of Osama bin Laden, the main suspect in the U.S. attacks.
As part of Britain's security crackdown, authorities this week at London's Heathrow airport have confiscated more than 20,000 knives, scissors, corkscrews, and other sharp objects from passengers' carryon baggage.
Elsewhere in Europe, police in Paris are holding seven people arrested Friday. Police are investigating potential terrorist attacks on U.S. interests in France.
In Germany, authorities have issued arrests warrants for two men suspected of having links with a hijacker, Mohamed Atta, on the first plane to hit the World Trade Center.