London, June 17: It is "only a matter of time" before terrorists stage a biological, chemical or nuclear attack on a Western city, the head of Britain's domestic intelligence agency MI5 said today. Speaking at a London think-tank, Eliza Manningham-Buller added Osama bin Laden's al-Qaeda network, responsible for the September 11, 2001 attacks in the United States, remained a "deadly" global threat.

"We are faced with a realistic possibility of a form of unconventional attack that could include chemical, biological, radiological or nuclear (CBRN) weapons," she told the Royal United Services Institute (RUSI).

"It is only a matter of time before a crude version of a CBRN is launched on a Western city," she said.

Intelligence suggests "renegade scientists" have given terrorists the information they need to create such weapons, although conventional bombs and suicide bomb attacks were still weapons of preference, she said.

On al-Qaeda, Manningham-Buller said: "They still remain an organisation capable of deadly terrorist attacks."

"The supply of potential terrorists among extreme elements is unlikely to diminish," she said. "Breaking the link between terrorism and religious ideology is difficult."

Manningham-Buller's remarks to the RUSI were her first on the record since she became director-general of MI5 in October last year.

Bureau Report