KABUL, Afghanistan — An American airstrike may have mistakenly killed at least 11 narcotics officers in southern Afghanistan on Sunday night, Afghan officials said on Monday. But the American military denied that such an airstrike had taken place.

The deputy interior minister for counternarcotics, Baz Mohammad Ahmadi, said that 11 officers from his agency had been killed and four wounded in an airstrike on an official convoy in the Garmsir District of Helmand Province. In a statement, he said that the convoy had been in the middle of an operation to arrest drug smugglers and that the operation had been coordinated with officials in Kabul and with the Helmand provincial government.

Mr. Ahmadi did not identify who carried out the airstrike. But Najib Danish, the deputy spokesman for the Interior Ministry, said it was by the NATO-led military coalition. Only American warplanes have been known to carry out bombing raids for the coalition in Afghanistan this year.

A police official in Garmsir District, speaking on condition of anonymity because he was not permitted to speak to the press, said the narcotics agents had disguised themselves as Taliban, who work closely with drug smugglers in that area. The officers used cars identical to the Taliban’s and flew the insurgents’ flags on them, he said, which may have fooled American warplanes into attacking. The official put the death toll at 15 officers.