British police are searching a number of properties following the arrest of two men in northern England under the country's security laws.
The men, aged 25 and 29, were arrested at separate locations in Halifax, northern England.
Police were examining four properties in Halifax and an address in north London. The arrested men are being taken to the capital for questioning later today.
Police have made hundreds of arrests under security laws since the September 11th attacks on the United States.
Britain suffered its worst peacetime attack on July 7th, 2005, when four suicide bombers blew themselves up on three London underground trains and a bus, killing 52 people and wounding more than 700.
Last November the country's domestic spy chief warned that Muslim extremists were plotting at least 30 major terrorist attacks in Britain.
Eliza Manningham-Buller, head of intelligence agency MI5, said young British Muslims were being groomed to become suicide bombers and that her agents were tracking some 1,600 suspects, most of whom were British-born and linked to al-Qaeda in Pakistan