US officials confirmed that they held preliminary talks during the summer of 2011 with representatives of the militant network at the request of the ISI.

Mehsud was the leader of the loosely-knit Pakistani Taliban, a militant network comprising 13 different, and sometimes rival, factions.

The new combat operation reflects the Pentagon's growing concern that militant Islamic networks pose an increasing threat to Americans in Southeast Asia.

But the chance to observe over the long term a militant Islamic network as it planned attacks on American interests and to make perhaps dozens of arrests was lost.

Pakistani forces uncovered a sign of the strength and sophistication of the militant network on Monday, officials said.

The proposed exercise reflects the Pentagon's growing concern that militant Islamic networks pose an increasing threat to Americans.

Bin Laden left "an invisible footprint" and he had not been contacting other militant networks.

The militant networks along the Afghan-Pakistan border are still interwoven with the global jihadists.

The Pentagon has also sharply expanded its intelligence work outside of war zones, sending Special Operations troops to embassies to gather information about militant networks.

Drone strikes and covert operations - conducted with or without the approval of the Pakistani authorities - can be directed against the militant network.