ISTANBUL/ADDIS ABABA, Dec 22 (Reuters) — U.S. authorities have taken issue with Turkey over its sales of armed drones to Ethiopia, where two sources familiar with the matter said there was mounting evidence the government had used the weapons against rebel fighters.

Washington has “profound humanitarian concerns” over the sales, which could contravene U.S. restrictions on arms to Addis Ababa, a senior Western official said.

The year-long war between Ethiopia’s government and the leadership of the northern Tigray region, among Africa’s bloodiest conflicts, has killed thousands of civilians and displaced millions.