The United States has estimated that some 500,000 people died in Ethopia's two-year conflict, making it one of the deadliest wars of the 21st century.
Ethiopia's government has accused the United States of unfairly apportioning blame for crimes committed during the two-year Tigray conflict.
The US allegations were "partisan," the foreign ministry said on Tuesday, adding: "The US statement is inflammatory".
Washington on Monday accused all parties to the conflict of committing war crimes.
But it singled out Ethiopian, Eritrean and regional Amhara forces for crimes against humanity, without mentioning the Tigrayan rebels.
US Secretary of State Antony Blinken, who last week made his first visit to Ethiopia since a breakthrough November 2022 peace deal between the federal government and Tigrayan rebels, on Monday made a forceful call for accountability on his return to Washington.
He said the State Department carried out a "careful review of the law and the facts" and concluded that war crimes were committed by federal troops from both Ethiopia and its ally Eritrea as well as by the rebel Tigray People's Liberation Front (TPLF) and forces from the neighbouring Amhara region.
"Many of these actions were not random or a mere byproduct of war. They were calculated and deliberate," Blinken said as he presented an annual rights report.
Blinken added that the State Department also found crimes against humanity by Ethiopian, Eritrean and Amhara forces, including killings and sexual violence, although he did not mention the TPLF.
Ethiopia's foreign ministry said the US statement "unfairly apportions blame among different parties in the conflict."
"The statement appears to exonerate one party from certain allegations of human rights violations such as rape and other forms of sexual violence despite the clear and overwhelming evidence about its culpability," it said.
"This partisan and divisive approach from the US is ill-advised," it added, calling it "unwarranted".
TPLF officials did not respond to AFP news agency requests to comment about the US report.
Blinken had called for accountability during his trip to Addis Ababa, where he held an unusually long meeting with Prime Minister Abiy Ahmed and spoke separately with senior TPLF leader Getachew Reda.
But he did not directly mention war crimes or crimes against humanity and sounded upbeat about the prospects for peace during his visit.
READ MORE: Blinken asks Ethiopia to strengthen peace on first post-war visit
The war badly soured US relations with Ethiopia, Africa's second most populous nation and long one of Washington's major partners on the continent.
Abiy had earlier voiced anger when Blinken during the war spoke more generally about crimes against humanity, and the Ethiopian leader has rejected UN-led efforts for a probe.
On Tuesday, the foreign ministry said Washington's statement "undercuts the support of the US for an inclusive peace process".
The war began in November 2020 when the TPLF, once the major powerbroker in Ethiopia, attacked federal military installations in the Tigray, triggering a major counteroffensive.
As allegations of atrocities mounted, the US imposed sanctions on Eritrea, an authoritarian state whose relations with Washington were already poor, and booted Ethiopia from a major trade pact, although it held back on further actions against the warring parties.
READ MORE: Blinken in Ethiopia to repair ties as Russia, China boost Africa influence