Mark Sedwill, senior civilian representative for the Western military alliance in Afghanistan, said Pakistani attitudes were hardening toward guerrilla groups that had previously been supported by the state.
"In the past, they had relations with various groups," he told the Asia Society think tank in New York, but now "I think there has been a shift."
However, there are limits on what Pakistan can do to stem the flow of militants entering Afghanistan to fight NATO troops.
"To be honest, the Pakistanis are preoccupied with those domestic threats. This is out of hand," Sedwill said.
"People sometimes say the Pakistanis must do more.... (but) actually they have lost an awful lot of soldiers fighting the groups that target them," he said. "They have their hands full."
Sedwill said Western governments should resist seeking quick pressure against the Pakistani government.
"If we just say we'll either bestow or withdraw a favor, then they'll turn to someone else. We've seen that in the past," he warned.
