LONDON, England (CNN) -- The head of Britain's intelligence services has warned that children as young as 15 are becoming involved in terrorist-related activity.
Jonathan Evans, the chief of MI5, also said that at least 2,000 people in Britain pose a threat to the country's security because of their support for al Qaeda-inspired terrorism.
"As I speak, terrorists are methodically and intentionally targeting young people and children in this country. They are radicalising, indoctrinating and grooming young, vulnerable people to carry out acts of terrorism," he told a gathering of newspaper editors in Manchester.
Evans said the figure of 2,000 -- an increase of 400 since November 2006 -- only included those the intelligence services knew about and that the actual number could be double.
He said there had been 200 terrorist convictions in Britain since the September 11 attacks.
The MI5 head added that over recent years much of the command and inspiration for attack planning in the UK had come from al Qaeda's remaining core leadership in the tribal areas of Pakistan.
However, he said in the last 12 months terrorist plots on British soil were increasingly inspired by al Qaeda cadres in other countries, including in Iraq and East Africa.
"There is no doubt now that al Qaeda in Iraq aspires to promote terrorist attacks outside Iraq. There is no doubt that there is training activity and terrorist planning in East Africa -- particularly in Somalia -- which is focused on the UK," he told the Society of Editors meeting.
According to Evans, there had been "no decrease" in the number of Russian covert intelligence officers operating in Britain since the end of the Cold War.
He said that resources that could be devoted to counter-terrorism were instead being used to protect Britain against spying by Russia, China and others.
"A number of countries continue to devote considerable time and energy trying to steal our sensitive technology on civilian and military projects and trying to obtain political and economic intelligence at our expense," he said. E-mail to a friend