WASHINGTON — The deadly U.S. attack on a hospital in Afghanistan, which U.S. officials have called a “mistake,” leaves open the possibility that the decision to open fire exceeded the authority under which American forces have operated since their combat mission ended nearly a year ago, officials say.

U.S. officials have declined to discuss most circumstances of the attack in Kunduz that killed 22 civilians, since American and Afghan investigations are under way.

Gen. John Campbell, the top U.S. commander in Afghanistan, told a Senate committee on Tuesday that he is requiring that every U.S. service member in Afghanistan be retrained on the circumstances in which U.S. firepower can be used.

Campbell did not elaborate, but his statement pointed to the possibility that the U.S. attack was undertaken in error, even if the target had not been a hospital and there had been no civilian casualties.

Campbell said Afghan forces fighting to retake Kunduz from the Taliban had requested U.S. air power, and that a U.S. special operations unit in the “close vicinity” was communicating with the crew of the heavily armed AC-130 gunship that pummeled the hospital.

U.S. forces do not have blanket authority to fulfill every Afghan request for U.S. firepower.