By Phil Stewart

Blinken’s statement suggested growing frustration with the response so far from Ethiopia and neighboring Eritrea to what America’s top diplomat described as a “worsening humanitarian crisis.”

His remarks came a day after Amnesty International released a report accusing Eritrean forces of killing hundreds of civilians in Tigray in a 24-hour period last year, an incident it described as a potential crime against humanity.

Eritrea rejected the accusations.

“The United States is gravely concerned by reported atrocities and the overall deteriorating situation in the Tigray region of Ethiopia,” Blinken said.

“We ask international partners, especially the African Union and regional partners, to work with us to address the crisis in Tigray, including through action at the U.N. and other relevant bodies.”

On Sunday, Ethiopia’s foreign ministry said in a statement that pronouncements by the United States on Ethiopia’s internal affairs were “regrettable”.

“It should be clear that such matters are the sole responsibility of the Ethiopian government, which as a sovereign nation, is responsible to deploy the necessary security structures and means available in ensuring the rule of law within all corners of its borders,” the ministry said in a statement posted on Facebook.

Ethiopian Prime Minister Abiy Ahmed’s federal army ousted the former local ruling party, the Tigray People’s Liberation Front (TPLF), from the regional capital Mekelle in November, but low-level fighting has continued.

Thousands of people have died, hundreds of thousands have been forced from homes and there are shortages of food, water and medicine around the region of more than 5 million people.

Ethiopia and Eritrea have denied that Eritrean troops participated in the conflict, though dozens of witnesses, diplomats and an Ethiopian general have reported their presence.

Still, the state-run Ethiopian Human Rights Commission released a statement on Friday timed to coincide with the Amnesty report, saying preliminary investigations indicated that Eritrean soldiers had killed an unknown number of civilians in Axum, an ancient city in northern Ethiopia. It said the killings were in retaliation for an earlier attack by TPLF soldiers.

Amnesty said Eritrean soldiers executed men and boys in the streets and engaged in extensive looting.

Blinken noted Ethiopian commitments to full accountability, including international support for investigations into human rights abuses and to allowing unhindered humanitarian access.

“The immediate withdrawal of Eritrean forces and Amhara regional forces from Tigray are essential first steps,” Blinken said.

“They should be accompanied by unilateral declarations of cessation of hostilities by all parties to the conflict and a commitment to permit unhindered delivery of assistance to those in Tigray.” (Reporting by Phil Stewart; Additional reporting by Nairobi Newsroom; Editing by William Mallard)