According to the CIA, which has recruited a number of informants in the Pakistani community, a British extremist of Pakistani origin entering the US is the most likely source of a terror attack on America, Britain's leading newspaper 'The Sunday Telegraph' reported.

A former CIA officer who has advised President Barack Obama, told the British newspaper that the agency has in fact stepped up its efforts after the Mumbai mayhem "laid bare the threat from Lashkar-e-Taiba", the militant group which has an extensive web of supporters in UK's Pakistani community.

"In the aftermath of the Mumbai attack the US and the UK intelligence services now have to regard Lashkar-e-Taiba as just as serious a threat to both of our countries as al-Qaeda.

They have a much more extensive base among Pakistani Diaspora communities in the UK than al Qaeda," Bruce Riedel said.

The CIA has already briefed President Barack Obama about the threats, according to Riedel, who served three US presidents as a Middle East expert on the White House National Security Council.

Riedel said: "The British Pakistani community is recognised as probably al-Qaeda's best mechanism for launching an attack against North America.

"The American security establishment believes that danger continues and there's very intimate cooperation between our security services to monitor that. The Americans run their own assets in Pakistani community they get their intelligence.