The United Nations high commissioner for human rights called on Ethiopia to permit an investigation into allegations of murders and sexual violence in the Tigray region, which may amount to war crimes.

“We urge the government of Ethiopia to grant my office and other independent monitors access to the Tigray region, with a view to establishing the facts and contributing to accountability, regardless of the affiliation of the perpetrators,” Michelle Bachelet said Thursday in a statement.

Federal troops deployed by Prime Minister Abiy Ahmed have been fighting forces of the region’s former ruling party, the Tigray People’s Liberation Front (TPLF). Thousands of people have been killed in the area where hundreds of thousands of people were dependent on food aid before the conflict began, according to the U.N.

“A preliminary analysis of the information received indicates that serious violations of international law, possibly amounting to war crimes and crimes against humanity, may have been committed by multiple actors in the conflict,”  Bachelet said.

In addition to the TPLF, Bachelet cited the Ethiopian National Defense Force, Eritrean armed forces, and Amhara regional forces and affiliated militia as suspected perpetrators of the alleged murders and sexual assaults.

Abiy’s government, the Tigray administration, and the TPLF did not immediately comment on the human rights chief’s statement. The prime minister’s office, however, said “no individual or entity, nationally or internationally, is above the laws of the land,” in a statement issued on March 3 addressing reports of human rights violations in Tigray region.

Bachelet’s call for an investigation also follows separate reports by Amnesty International and U.S. cable news channel CNN, about massacres allegedly committed by Eritrean troops in the city of Axum and the ancient church of Maryam Dengelat. Amnesty also found that Ethiopian forces may have committed war crimes. Additionally, multiple victims and eyewitnesses in Axum spoke to VOA’s Tigrigna service in January .

“The U.N. high commissioner’s statement today underscores the gravity of the alleged crimes being committed by all sides in the Tigray conflict, and the urgency of the U.N. acting now,” said Sarah Jackson, Deputy Regional Director for East Africa at Amnesty International.

The U.N. Security Council met behind closed doors Thursday to discuss the situation but issued no statement afterwards.

The U.S. ambassador to the U.N. expressed alarm about the humanitarian and human rights situation in brief remarks to reporters after the meeting, saying it poses a direct threat to regional peace and security.

“The onus to prevent further atrocities and human suffering falls squarely on the Ethiopian government’s shoulders,” Linda Thomas-Greenfield said virtually. “We urge the Ethiopian government to support an immediate end to the fighting in Tigray. And to that end, the prompt withdrawal of Eritrean forces and Amhara regional forces from Tigray are essential steps.”

She urged the broader region to work together quickly to reach a peaceful solution.

Thomas-Greenfield said the United States is committed to working bilaterally and multilaterally to help end the violence and to hold perpetrators of abuses on all sides accountable.

U.N. humanitarian chief Mark Lowcock urged the council to scale up humanitarian assistance to Tigray immediately. Official estimates put the number of people in need at about 4.5 million.

Diplomats said he warned of the possibility of famine if large-scale aid deliveries do not reach people quickly, particularly in remote areas. Food insecurity is rising, as both harvests and markets have been disrupted by the conflict.

Lowcock also urged the withdrawal of Eritrean troops, telling council members that it is “now abundantly clear to all” that Eritrean Defense Forces are operating across Tigray, where there are numerous confirmed reports of atrocities they have carried out.

As fighting in Tigray enters its fifth month, journalists have started returning to the region of about 5 million people, after being barred since the war began in early November. But advocates raise concerns with recent intimidation and detention of local journalists and translators.