KABUL, Afghanistan — An operation by Afghan and American forces in the southern Afghan province of Helmand has left at least a dozen civilians dead, officials and residents said on Wednesday, illustrating the plight of noncombatants caught in the middle of the 17-year conflict.

Afghan and Western officials said that Afghan special forces had come under heavy fire overnight during an operation against the Taliban in the Garmsir district and had requested American airstrikes against Taliban fighters.

But on Wednesday, the officials acknowledged that civilians had also been struck. One Western official said that 13 civilians had been killed, in addition to 16 members of the Taliban. Residents of Garmsir put the number of civilians killed at 22.

Ghafoor Ahmad Jawed, a spokesman for the Ministry of Defense, said it had received reports of civilian casualties but could not elaborate on numbers. He said a delegation had been sent to Helmand to investigate.