Spy chief says MI5 tracking 30 plots

British authorities are tracking about 30 terrorist plots involving 1,600 suspects, the country’s domestic spy chief said, warning that young British Muslims are at risk of being radicalized by extremists.

It was the first public estimate of the threat by the head of the Security Service, Eliza Manningham-Buller, who said her agency and police were monitoring 200 cells engaged in plotting or aiding attacks in Britain and abroad.

Manningham-Buller said the Security Service -- MI5 -- had foiled five major plots since London transit attacks in July 2005 that killed 52 commuters and the four suicide bombers.