Pakistani troops fire on intruding U.S. choppers

Pakistani troops fired on two U.S. helicopters that intruded into Pakistani territory on Sunday night, forcing them to turn back to Afghanistan, a senior security official with knowledge of the clash said on Monday. (Graphic/Reuters)

It was the second such incident in a week, and reflects frayed relations with the United States over Pakistan's failure to act more forcibly against Islamist fighters in the tribal lands bordering Afghanistan.