A file photo shows US State Department spokesman Ned Price during a press conference at the State Department in Washington, DC. AFP
Survivors told AFP that hundreds of people belonging to the Amhara ethnic group were killed over the weekend by rebels in the Oromia region, with bodies still lying on the streets after hours of violence.
State Department spokesman Ned Price said the United States was "gravely concerned" by "this horrific act."
"We also call on all Ethiopians to reject violence, and instead, pursue peaceful dialogue to resolve differences," Price said in a statement.
"National reconciliation must involve comprehensive, inclusive justice for victims and accountability for those responsible for human rights abuses and violations."
The Oromia regional authorities said the attack was carried out by the Oromo Liberation Army, which is branded as a terrorist organization by the Ethiopian government.
But a spokesman for the rebel group blamed the region's own pro-government militia for the killings and called for an independent investigation.
The violence comes despite guarded hope for a return to peace in northern Ethiopia, where a war that broke out in November 2020 has horrified rights groups and foreign governments, with the United States ending preferential trading status for its longtime ally.
Ethiopia's government declared a humanitarian truce in March, allowing limited supplies of international aid into Tigray for the first time since mid-December.