NATO says it is investigating an incident that occurred along the border between Afghanistan and Pakistan, in which its helicopters were accused of killing 25 Pakistani soldiers.
Pakistani officials on Saturday accused the U.S.-led coalition of firing on Pakistan army checkpoints.
In retaliation, the Pakistan government closed a key border crossing that NATO uses to move supplies to the war in neighboring Afghanistan.
Top NATO and U.S. commander in Afghanistan Gen. John Allen issued a statement Saturday offering condolences to any members of the Pakistan security forces who might have been killed or injured.
But the coalition did not claim any responsibility for their deaths, saying that the incident is still being investigated.