Rebels from Ethiopia's northern Tigray region have taken control of the UNESCO World Heritage city of Lalibela in the neighboring Amhara region.
Home to 13th-century rock-hewn churches, Lalibela is a holy place for millions of Orthodox Christians.
Residents were fleeing the insurgent attack, local officials told the BBC.
Thousands of people have been killed since the war began last November. Fighting is now spreading to Amhara and Afar, another region bordering Tigray. Millions have been displaced.
Both the Tigray rebel forces and the Ethiopian army and its allies have been accused of human rights violations and war crimes.
The deputy mayor of Lalibela, Mandefro Tadesse, told the BBC that the city was under the control of Tigrean rebels.
He said there was no shooting, but residents were fleeing the city and he was concerned about the safety of historic churches.
"This is a world heritage and we must work together to guarantee the preservation of this treasure," he said.
Washington has become increasingly concerned about the conflict, and the US State Department has called on Tigrean forces to respect Lalibela's cultural heritage.
In Lalibela there are 11 medieval monolithic rock-cut rock churches dating from the 12th and 13th centuries. They were built as a substitute for pilgrimages to the Holy Land, which was unreachable at the time. The churches were declared a UNESCO World Heritage Site in 1978. The priests of the Ethiopian Orthodox Church Tevahedo take care of them.
The widespread fighting followed significant territorial gains made by the rebel Tigray People's Liberation Front (TPLF) in June, including the capture of the Tigray regional capital Mekele after Ethiopian troops withdrew and the government declared a unilateral ceasefire.
The TPLF was the regional government of Tigray until it was ousted by federal forces last November. It has been designated a terrorist organization by the Ethiopian government. However, the rebels say they are the legitimate regional government of Tigray.
Earlier this week, a rebel general told the BBC that the group aims to force the federal government to lift its blockade of the region and agree to a political solution to the crisis.
The government denies the existence of the blockade and has ruled out talks.
However, the TPLF's inroads into Amhar and Afar have drawn international criticism, with both the United Nations and the US this week calling on all sides to stop fighting.
The Ethiopian government says more than 300.000 people have been displaced in Amhara and Afar.
The UN said separately that 175 trucks with humanitarian aid had arrived in Tigray. However, the head of the UN's World Food Program warned that more than 100 trucks a day are needed to reach the millions in need.
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