U.S. military says Pakistan not targeting U.S. troops

WASHINGTON (Reuters) - The day after U.S. and Pakistani forces exchanged fire along the Afghan border, the top U.S. military officer said on Friday he was comfortable Pakistani troops had not been told to shoot at American forces.

Navy Adm. Mike Mullen, chairman of the U.S. Joint Chiefs of Staff, said he received assurances from the Pakistani military leadership during a visit to Pakistan last week and appealed for calm in the face of "hair-trigger tension" over the Afghanistan-Pakistan border region.

But Mullen, top military adviser to President George W. Bush and Defense Secretary Robert Gates, said he had not spoken to Pakistani officials since the exchange of fire occurred.

"I've been given assurance by the senior military leadership in Pakistan that there is certainly no intent or plan to fire on our forces," Mullen told reporters.

"I find no need, based on my discussions and the assurances so far, to pick up the phone and talk to (Pakistani military leaders) to see if we're not understanding each other."

Pakistani forces opened fire on Thursday on two U.S. helicopters that U.S. officials said were supporting a U.S.-Afghan ground patrol inside Afghanistan's Khost Province. Pakistani officials said their forces fired warning shots after the helicopters entered Pakistan air space.

U.S. and Afghan forces shot back and an exchange of fire ensued. No one was injured.

"Because of the proximity and the difficulty of the terrain, it can be tough and there can be misunderstandings," Mullen said. "It doesn't mean we should ever overreact to the hair-trigger tension we are all feeling. Now more than ever is a time for teamwork, for calm."

Thursday's shooting was the latest in a series of incidents that have ratcheted up tensions in the border region, where the United States has been targeting Islamist militant safe havens blamed for growing violence in Afghanistan.

Unmanned U.S. aircraft have carried out missile strikes on militant targets in Pakistan. On September 3, U.S. commandos raided a suspected al Qaeda target in South Waziristan.

The attacks have stirred protests from Pakistani military and civilian leaders.

There have also been disputed reports about ground fire from Pakistan turning back U.S. helicopters and downing an unmanned U.S. surveillance drone.

Mullen said escalating tensions would not dissuade the United States from protecting its forces in Afghanistan.

"I don't think the U.S. will be constrained at all in protecting its troops," he said. "It's a pretty tense place. The safe haven has gotten safer this year. The insurgency has gotten more sophisticated."

The United States has about 33,000 U.S. troops in Afghanistan, including 13,000 who operate under NATO command.

(Editing by Kristin Roberts and Peter Cooney)