Washington, Dec 10 (IANS) Citing the case of David Headley charged with helping to plan Mumbai terror attacks, a top US counter-terrorism official has warned of the danger from home grown terrorists, many of them trained in Pakistan.

The Al Qaeda terrorist group blamed for the Sep 11, 2001 attacks was in disarray, under pressure in Afghanistan-Pakistan and ideologically discredited with only real sparks of hope in "under-governed" places like Yemen and Somalia, Daniel Benjamin, the State Department counter-terrorism chief said Wednesday.

But a "second arena where Sunni radicals continue to succeed is in persuading religious extremists to adopt their cause, even in the United States," he said at a Jamestown Foundation conference citing the Headley and a couple of other cases.

"A bus driver, Najibullah Zazi, was trained in Pakistan and now faces charges in federal court for planning to set off a series of bombs in the United States," he noted .

"An indictment that was unsealed Monday in Chicago portrays an American citizen - David Headley - playing a pivotal role in last year's attack in Mumbai, which killed more than 170 people and dramatically raised tensions in South Asia."

"So even if this radical movement is not mobilising the masses, it is still galvanising enough people to take to violence and poses a continuing, powerful threat," said Benjamin.

"The importance of these two cases should not be glossed over - the conspiracies these men were engaged in had roots in the FATA (Pakistan's Federally Adminstered Tribals Areas), and eight years after 9/11, should give us all pause," he said.

"The threat to the US remains substantial and enduring despite the operational constraints on Al Qaeda central."

"It is also multifaceted as we have seen in the movement of young men, many of them motivated by a sense of ethnic duty, who have left their communities in Minnesota, been radicalised in Somalia, and fought and died for al-Shabaab," the official said.