Fears of a new war in the Horn of Africa are rising as Ethiopia and Eritrea take their dispute to the United Nations.

Ethiopia told the U.N. Security Council on Friday that it is taking measures in self-defense against Eritrea, the Associated Press reported via Newsday. Foreign Minister Gedion Timothewos invoked Article 51 of the U.N. Charter, which covers self-defense. He did not say what measures Ethiopia is taking.

Ethiopia accuses Eritrea of sending infantry and armored units across the border in recent weeks, DW reported. It also says Eritrea is backing, arming and directing rebel groups. In a letter dated Oct. 8, Gedion said Eritrean forces had pushed up to 60 kilometers into Tigray, Mereja reported, citing Reuters.

On Saturday, Eritrean Foreign Minister Osman Saleh rejected the accusations. In his own letter, he asked the Security Council to "forcefully condemn" Ethiopia and called for steps to deter it, DW reported.

On the ground, AP footage on Saturday showed Ethiopian military vehicles and troops entering Adigrat, about 25 kilometers from the Eritrean border. Some residents celebrated in the streets. People in the city described hunger, closed banks and a lack of medical care.

Tigray was devastated by a 2020-2022 war between Ethiopia's government and Tigrayan forces. Eritrean troops fought on Ethiopia's side then, and hundreds of thousands of people died.

Ethiopia's Prime Minister Abiy Ahmed has also spoken of wanting access to the Red Sea, which Eritrea sees as a threat. Diplomats fear a new war could pull in other countries in the region.

What we know: Ethiopia told the U.N. Security Council it is acting in self-defense against Eritrea, which rejected the claims.
What we don't: What measures Ethiopia is taking, and whether the fighting will spread.