ISLAMABAD — Pakistan's army on Monday formally rejected a U.S. claim that American airstrikes that killed 24 Pakistani troops last year were justified as self-defense, a stance that could complicate efforts to repair the troubled but vital relationship between the two countries.

In a detailed report, the army said that Pakistani troops did not trigger the Nov. 26 incident at two posts along the Afghan border by firing at American and Afghan forces, as the U.S. has alleged. Pakistan's army said its troops shot at suspected militants who were nowhere near coalition troops.

"Trying to affix partial responsibility of the incident on Pakistan is, therefore, unjustified and unacceptable," said the report, which was issued in response to the U.S. investigation that concluded at the end of December.

The U.S. expressed condolences for the deaths of the Pakistani soldiers but said American troops acted "with appropriate force" in self-defense because they thought they were being attacked by Taliban insurgents.

Pakistan responded almost immediately to the incident by closing its border crossings to supplies for NATO troops in Afghanistan. The borders have remained closed, and Pakistan also kicked the U.S. out of a base that was used to service American drones.