The top U.S. military officer says Pakistan is justified in being angry about NATO airstrikes that killed 24 Pakistani soldiers in a Pakistani-Afghan border region, but he declined to apologize, citing the need for an investigation.

In an interview with British television network ITV broadcast late Monday, U.S. Joint Chiefs of Staff Chairman General Martin Dempsey says Islamabad has a “reason to be furious” that the weapons that killed the Pakistani troops on Saturday were the “ordinance of a partner.”

Speaking on a visit to London, General Dempsey said he would like to “enlist” the Pakistani government's patience to “find out what happened” in the incident, in which NATO aircraft struck several Pakistani border posts. The airstrikes happened in an area of poorly-marked and disputed borders between Afghanistan's Kunar province and the Pakistani tribal region of Mohmand.

The U.S. military said Monday an Air Force general will lead an investigation of the incident and compile an initial report by December 23rd. It says Brig. Gen. Stephen Clark will work with representatives of NATO and the Afghan and Pakistani governments to determine how to prevent similar situations in the future.

Pakistani Prime Minister Yousuf Raza Gilani said Monday relations with the United States are no longer “business as usual” following the killings of the Pakistani soldiers. In an interview with U.S. television network CNN, Mr. Gilani said Pakistan is not receiving the “mutual respect” that he says is necessary for the U.S. relationship to continue.

NATO and Afghan officials say their troops called in NATO airstrikes in response to incoming fire from areas near the Pakistani border posts. Pakistan's army spokesman, Major General Athar Abbas, denied that Pakistani troops fired first and accused the NATO and Afghan officials of making excuses.

The Associated Press quotes unnamed U.S. officials as saying military investigators believe Taliban militants attacked a U.S.-Afghan patrol in the border region to try to create confusion and draw U.S. and Pakistani forces into firing on each other.

The Pakistani government responded to the incident by shutting down NATO's Pakistani supply routes into Afghanistan and ordering U.S. personnel to evacuate an air base in the Pakistani province of Baluchistan within two weeks. Experts believe the U.S. Central Intelligence Agency has been using the Shamsi air base to launch drones that patrol and fire missiles on militant targets in Pakistani-Afghan border regions.

In his interview, General Dempsey says U.S.-Pakistani relations are “on about as rocky a road as I have seen.” But, he said the situation is not irretrievable and military-to-military ties remain “solid” due to common interests such as fighting terrorism.