KABUL, Afghanistan — At least 30 civilians were killed by American airstrikes that targeted drug labs in western Afghanistan this spring, according to a United Nations report released on Wednesday, a figure that the United States-led mission in the country quickly disputed.

The strikes, on May 5, targeted more than 60 sites in Farah Province and neighboring Nimruz Province, the United Nations report said. As of last month, the United Nations Assistance Mission in Afghanistan had verified that 39 civilians were either wounded or killed in the strikes. Seventeen of those were working in the drug labs, which were primarily producing methamphetamine.

A statement from the American-led mission in Afghanistan disagreed with nearly all of the report, citing its “reliance on sources with conflicted motives” and the decision to call those killed in the bombings civilians instead of insurgents.

The dispute sheds light on America’s current war methods — relying heavily on overhead surveillance, air support and local forces to select and attack targets — and the sometimes contentious definitions by which the United States military identifies combatants on an increasingly murky battlefield.