(CNN) Fighters from Ethiopia's war-torn Tigray region have seized control of a UN World Heritage Site in a neighboring region, Reuters and AFP reported, citing eyewitnesses.
Lalibela is home to 11 medieval monolithic churches that were carved out of rock some 900 years ago. The churches are a holy site for millions of Ethiopian Orthodox Christians.
Some residents fled the town, located in Ethiopia's Amhara region, as the Tigrayan fighters arrived, Reuters reported on Thursday.
The United States has called on the fighters to "protect this cultural heritage," State Department spokesman Ned Price said Thursday.
CNN was not able to independently verify the reports that Lalibela was captured by Tigrayan fighters.
The Ethiopian government on Friday threatened that it would be forced to respond to Tigrayan forces if they continue to expand into neighboring regions, a statement from the Ministry of Foreign Affairs said.
"The action of the irresponsible group is testing the Federal Government's patience and pushing it to change its defensive mood which has been taken for the sake of the unilateral humanitarian ceasefire," the statement read.
The statement added that the Ethiopian government is "being pushed to mobilize and deploy the entire defensive capability of the state if its humanitarian overtures for a peaceful resolution of the conflict remain unreciprocated," and accused Tigrayan fighters of launching "new attacks in the neighboring regions of Amhara and Afar, which left more than 300,000 people displaced and thousands dead."
A second statement directly addressed the reported spillover of the conflict into Amhara, saying people were concerned about possible destruction of religious and cultural institutions by Tigrayan forces.
"The government will take all the necessary measures to ensure that these sacred places and other institutions are well protected and call on the international community to condemn this heinous act of the TPLF," it said.
The developments come eight months after Ethiopian Prime Minister Abiy Ahmed launched a military offensive against Tigray's ruling party, the Tigray People's Liberation Front (TPLF), sending in national troops and militia fighters from the Amhara region who were joined by forces from neighboring Eritrea.
The war took a major turn when Tigrayan fighters recaptured their regional capital of Mekelle from Ethiopian forces in June, then rejected a last-minute ceasefire offer from the central government.
Since then, the fighting has spread, with TPLF fighters pushing from Tigray into the neighboring regions of Amhara and Afar.
CNN has contacted the Amhara regional government, the TPLF and UNESCO for comment on the reported capture of Lalibela.
On Thursday the US urged all sides in Ethiopia's conflict to avoid further escalations and to seek a ceasefire.
"We also call on all parties to the conflict to end the violence, as I said before, to initiate talks to achieve a negotiated ceasefire, and for the TPLF to withdraw its associated military forces immediately from the Amhara and Afar regions," Price added.
"At the same time, we renew our calls for the Amhara regional government to withdraw immediately its associated military forces from western Tigray, and for the Eritrean government to withdraw its military forces permanently from Ethiopia. All parties, as we've said, should accelerate unhindered delivery of humanitarian assistance to those affected by the conflict, and the commercial blockade of Tigray must come to an end
Asked about the reports regarding Lalibela, UN spokesman Stephane Dujarric said Thursday he had not gotten any information on this particular case but "we are aware that there's been a spillover" of the conflict beyond the Tigray region.
"Any conflict often starts out as small and, if it is not tended to, has a tendency to spill over and to get larger. And in the meantime, the people who are paying the price are the civilians," Dujarric said.
During a daily press briefing earlier on Thursday, Dujarric warned that although there has been a recent entry of aid and supplies into the Tigray "it is still insufficient, with an estimated 100 trucks needed every day to assist 5.2 million people in need."
"Trucks are going in, but we see trucks are looted. Trucks are also delayed," he added, referring to humanitarian aid food trucks.
He said that as of Wednesday, 175 trucks with humanitarian supplies, including food, non-food items and fuel had arrived in Tigray's capital Mekelle. "These include 50 trucks that crossed into Tigray over the past month with the remaining trucks crossing only in recent days," Dujarric said.
"These are among at least 223 trucks with humanitarian supplies for the UN and international NGOs that left Semera, the capital city of Afar Region, toward Mekelle. Most of the remaining trucks are being scanned at a checkpoint and a few trucks are in Abala, the last entry point into Tigray."
He said two trucks were reportedly blocked by civilians and looted at a checkpoint in Afar, 97 km from Semera, on July 28.