KABUL, Afghanistan — The American military claimed responsibility and expressed regret for an airstrike that mistakenly killed six members of a family in southwestern Afghanistan, Afghan and American military officials confirmed Monday.

The attack, which took place Friday night, was first revealed by the governor of Helmand Province, Muhammad Gulab Mangal, on Monday. His spokesman, Dawoud Ahmadi, said that after an investigation they had determined that a family home in the Sangin district had been attacked by mistake in the American airstrike, which was called in to respond to a Taliban attack.

Mr. Mangal summoned the American regional commander, Maj. Gen. Charles M. Gurganus of the Marines, to complain, and General Gurganus apologized, Mr. Ahmadi said.

A spokesman for the United States military in Helmand, Lt. Col. Stewart Upton, said, “We don’t have any issues with the governor’s statement.” He said American officials had been aware of the deaths and had immediately started an investigation.