KABUL, Afghanistan — Two NATO soldiers were killed Wednesday when men wearing uniforms of the Afghan security forces opened fire at an Afghan military base in the southern province of Helmand, the American-led international coalition said in a statement.

In other news highlighting the province’s precarious security, the strategic district of Musa Qala fell to the Taliban on Wednesday after fighting that lasted all night, members of the provincial council said. Officials had warned that if Musa Qala fell, the Taliban could tighten their grip on northern Helmand.

The nationalities of the NATO soldiers were not immediately clear. The statement released by the American-led coalition said the service members died when two men wearing Afghan uniforms opened fire on their vehicle. The attackers were killed when coalition forces returned fire, the statement said.

However, Afghan officials in Helmand said that the two NATO soldiers were part of a group of Americans. The officials said that the soldiers had been fired on by Afghan troops who suspected them of being Taliban fighters in army uniforms.