The suspects, aged from 17 to 28, had been under surveillance for weeks and were believed to have links to Pakistan and Bangladesh, security officials said.

The arrests come amid growing concerns in Europe over terrorism following a suicide bombing in Sweden and reported threats of a terror attack on a European city modeled on the deadly shooting spree in Mumbai, India.

Police swooped in before dawn on December 20 in coordinated raids on houses in four cities - London, the Welsh city of Cardiff and the English cities of Birmingham and Stoke-on-Trent.

The raid, a joint operation by Britain's domestic spy agency MI5 and police, was the largest since April 2009, when 12 men were detained over an alleged al-Qaida bomb plot in the northern city of Manchester.

AP