According to a senior Western official, Washington has "deep humanitarian concerns" about the transactions, which may violate US limitations on weaponry sales to Addis Abeba.

During a visit to Turkey last week, US Horn of Africa ambassador Jeffrey Feltman "addressed reports of armed drone use in Ethiopia and the attendant risk of civilian injury," according to a State Department spokesman.

According to a senior Turkish official, Washington expressed its displeasure at a few encounters. At the same time, neither the Ethiopian military nor the government responded to detailed demands for comment.

The United Nations agreed last week to establish an independent investigation into human rights violations in Ethiopia, a step strenuously opposed by the country's leadership.

Tigrayan rebel forces announced that they were evacuating from several northern regions in response to government gains. In a letter to the UN, they requested a no-fly zone above Tigray for drones and other hostile aircraft.

In May, the US State Department imposed restrictions on defence product exports to Ethiopia's armed forces.

In September, the White House authorised sanctions on people who indirectly engage in practices that endanger stability, exacerbate the crisis, or obstruct humanitarian assistance. However, no impending action against Turkey has been indicated.

The US Treasury, which has extensive economic punishment authority under that executive order, has declined to consider whether penalties should be imposed on Turkey.

According to a senior Turkish source, the foreign ministry investigated how drone sales would affect US foreign policy in the 2022 budget planning.

"The US has expressed its displeasure with Turkey's drone sales...but Turkey will continue to follow the policies it has established in this sector," the individual told Reuters.

According to a second senior Turkish defence ministry official, Ankara has no intention of interfering in any country's domestic affairs.

According to Exporters' Assembly figures, Turkish defence shipments to Ethiopia increased to about $95 million in the first 11 months of 2021, up from virtually nothing the previous year.

"Surveillance drones have a higher impact...and are beneficial," the individual said, adding that the conflict's nature rendered armed drones less useful.

When asked if other countries had contributed drone operators, the official replied, "I know Turkish guys were here at one point."

Turkish and Ethiopian officials have not publicly confirmed the sale of drones, which Reuters initially reported in October. The Turkish foreign ministry did not respond to a request for additional information.

Ethiopia has also purchased drones from the UAE, which did not respond to a request for comment on potential US concerns. Feltman was also set to visit the United Arab Emirates earlier this month.

Last year, the Turkish military utilised its Bayraktar TB2 drones in Syria, Libya, and Nagorno-Karabakh, sparking global interest in a market dominated by US, Chinese, and Israeli manufacturers.

In October, a representative for Turkey's foreign ministry stated that Ethiopia could obtain drones from any place. Last week, Foreign Minister Mevlüt Çavuşoğlu stated that engagement with Africa is founded for mutual benefit.

NATO allies Washington and Ankara have had difficult relations over several topics, including Turkey's acquisition of Russian missile defences and the United States' assistance for Kurds in northern Syria.

According to a State Department official, Feltman emphasised that "now is the time for all outside parties to urge discussions and the end of the war" in Ethiopia.

According to the Western official, who requested anonymity, Ankara responded to US concerns by attaching humanitarian restrictions to the Ethiopia agreement and requiring formal promises describing how drones will be deployed.