KABUL — Mistakes by both US and Pakistani forces led to airstrikes against Pakistani posts on the Afghanistan border that killed 26 Pakistani soldiers last month, according to a Pentagon investigation that for the first time acknowledged some American responsibility for the clash, which plunged the already frayed relationship between the United States and Pakistan to a new low. But a crucial finding — that the Pakistanis fired first — was likely to further anger Pakistan.
US officials said yesterday that the investigation, which has not yet been released, had concluded the airstrikes were an act of selfdefense ultimately justified because Pakistani soldiers opened fire on a joint team of Afghan and US special operations forces operating along the often poorly demarcated frontier between Afghanistan and Pakistan.