Extremists are grooming children and teenagers to plot terrorist attacks against Britain, the director of the domestic spy agency said Monday.

But Jonathan Evans, making his first public speech since becoming director-general of Britain's MI5 agency in April, said vital resources needed to tackle terrorism are being diverted to counter the espionage threat from Russia and China.

"Terrorists are methodically and intentionally targeting young people and children in this country," Evans said, according to a text of his speech in Manchester, England. "They are radicalizing, indoctrinating and grooming young, vulnerable people to carry out acts of terrorism."

Testimony from a U.S. terrorist-turned-witness in British court cases has revealed how young Britons are trained for attacks at terrorist camps in tribal areas of Pakistan.

Evans said though Pakistan remains a key training ground for Britons, similar centers are emerging elsewhere. Al Qaeda in Iraq is attempting to stage attacks outside Iraq and parts of East Africa, particularly Somalia, have become a key area for training and planning of attacks on Britain, he said.

Evans said thwarting plots alone is not enough to stop the threat of extremist terrorism, and urged the government and society to counter the message of radical preachers.

"If we only react tactically while our enemies plan strategically, we shall be hard put to win this. A key part of our strategy must be perseverance," Evans said at a newspaper editors' conference. "It starts with rejection of the violent extremist ideology across society."

He said Al Qaeda "has a clear determination to mount terrorist attacks against the United Kingdom."

But Evans warned that efforts to tackle terrorism are being stalled by work to halt foreign intelligence agents from stealing sensitive information on civilian and military technology. He singled out agents from Russia and China.

"So, despite the Cold War ending nearly two decades ago, my service is still expending resources to defend the U.K. against unreconstructed attempts by Russia, China and others, to spy on us," he said.

Officials at the Russian Embassy in London were not immediately available for comment.