State Department spokesman Ned Price said Washington was calling on the Ethiopian government and Tigrayan forces to “halt immediately their military offensives and to pursue a negotiated settlement” through African Union diplomacy.
On Wednesday, 10 people were killed in a second day of air strikes on the country's Tigray region when twin drone attacks hit a residential district in the regional capital of Mekelle.
The attack came shortly after rebels said they were willing to observe an immediate ceasefire and participate in a peace process led by the AU after about two years of war.
Mike Hammer, the US special envoy to the Horn of Africa, has been speaking to the Ethiopian government, the Tigray People's Liberation Front (TPLF) and UN and AU diplomats on the ground for two weeks.
“We are increasingly concerned by the growing military activity in northern Ethiopia. We strongly condemn the resumption of hostilities,” said Mr Price on Thursday.
“These actions are inconsistent with the government of Ethiopia and Tigrayan regional authorities' stated willingness [for peace talks],” he said.
The Ethiopian government said on Wednesday that it was “committed” to the AU-led peace process.
However, the two sides have blamed each other for the resumption of fighting in late August, which shattered a five-month truce that had allowed the delivery of aid.
An untold number of civilians have died, with the US alleging “ethnic cleansing,” since war broke out in late 2020 between the central government and the TPLF, which ruled Ethiopia for decades until Prime Minister Abiy Ahmed took office in 2018.