The Obama Administration has no count of Americans training overseas with Al Qaeda or other terrorist groups, but is gathering information with Pakistan and other governments to identify and locate people holding US passports who are receiving terrorist training then legally returning to commit violent acts, according to a top US diplomat.

Speaking to the Pacific Council on International Policy in Los Angeles, Ambassador to Pakistan Anne Patterson gave a "nightmare scenario" in which people holding US passports receive terrorist training then return legally to the US to commit violent acts.

"They can easily infiltrate back into the United States and, frankly, we don't know what to do about them. We think there are more out there than we know about. We just have to keep working at it," FOX News quoted Patterson, as saying.

Patterson said the US is gathering information with Pakistan and other governments to identify and locate such people.

Earlier, National Intelligence Director Dennis Blair reaffirmed what officials have learned from Nigerian terror suspect Abdulmutallab and had warned that al Qaeda's pool of suicide bombers may include US citizens and that the terror group may be targeting Americans overseas for attacks.

Testifying before the House Permanent Select Committee on Intelligence, Blair said that while the United States has ramped up its efforts against al Qaeda, it is becoming increasingly difficult to identify the group's immediate plans.

Blair told the Senate Intelligence Committee Tuesday that an al Qaeda attempt against the United States "is certain," when asked about the possibility of it happening in the next three to six months. (ANI)