Rebels from Ethiopia’s northern Tigray region have captured the town of Lalibela, a UNESCO World Heritage Site in the neighboring Amhara region.
Lalibela, home to 13th century rock-cut churches, is a sacred site for millions of Orthodox Christians.
Local officials told the BBC that residents were fleeing the rebel advance.
Thousands have died since the war broke out last November. Fighting is now spreading to Amhara and Afar, another area on the Tigray border.
Millions of people have also been displaced.
The Tigrayan rebel forces and the Ethiopian army and its allies have been accused of human rights abuses and war crimes.
The deputy mayor of Lalibela, Mandefru Tadesse, told the BBC that the city was under the control of the Tigray rebels.
There was no shooting, he said, but residents fled the town and he was concerned about the safety of the historic churches.
There are 11 medieval cave churches carved out of the rocks from the 12th and 13th centuries. They were built as an alternative to a pilgrimage to the Holy Land, which was inaccessible at that time.
“This is the heritage of the world, and we must cooperate to ensure that this treasure is preserved,” said Mr. Mandefrue.
The spread of fighting followed significant territorial gains made by the rebel Tigray Liberation Front in June, including the capture of Mekele, the capital of Tigray province, after the withdrawal of Ethiopian troops and the government’s unilateral declaration of a ceasefire.
The Tigray People’s Liberation Front 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 rebellious general told the BBC that the group aimed to force the federal government to lift the blockade of the region and agree to a political solution to the crisis.
The government denies there is a blockade and has ruled out talks.
But the TPLF’s rush to Amhara and Afar drew international criticism, and both the United Nations and the United States this week called on all sides to stop the fighting.
The Ethiopian government says more than 300,000 people have been displaced in Amhara and Afar.
Separately, the United Nations said that 175 trucks carrying humanitarian aid had arrived in Tigray.
But the head of the United Nations World Food Program has warned that more than 100 trucks are needed every day to reach the millions in need.
Aid workers struggled to reach a large part of Tigray due to insecurity and bureaucratic obstacles.
More on the Tigray crisis: