Eritrea's government has accused Ethiopia of launching an attack on its territory, but the extent of the assault was still unclear and there was no immediate response from Ethiopia.
A resident on the Ethiopian side of the border reported hearing the sound of explosions on Sunday and saw Ethiopian troops moving in the area. Eritrea, which won independence from Ethiopia in 1991, fought a bloody border war with its larger neighbour between 1998 and 2000. Tensions between the Horn of Africa nations persist.
"The TPLF regime has today, Sunday 12 June 2016, unleashed an attack against Eritrea on the Tsorona Central Front," the information ministry said in a statement around midnight.
TPLF refers to Ethiopia's Tigrayan People's Liberation Front, one of the four parties making up the ruling coalition. Tsorona Central Front is region of military command around the town of Tsorona, south of Eritrea's capital Asmara and close to the border. The area saw intense fighting during the border war that killed about 70,000 people.
"The purpose and ramifications of this attack are not clear," the Eritrean statement said.
A resident in the Ethiopian town of Zalambessa, across the border from Tsorona, told Reuters by telephone that he had heard the sound of shelling on Sunday and into the night.
"It did not stop until this morning around 9am (0600 GMT)," he said, asking not to be identified. He added that he had seen Ethiopian military vehicles and troops moving along the central stretch of the militarized border.
Eritrean information minister Yemane Ghebremeskel had no immediate additional comment when asked about casualties or other details of the attack. Ethiopian government officials were not immediately reachable for comment.
Charlotte King, senior Africa analyst at the Economist Intelligence Unit, said it was unusual for Eritrea to comment on flare ups but said the release may have been prompted by UN criticism Eritrea has faced over its prolonged national service. The UN accuses Eritrea of rights abuses for indefinite national service, where Eritreans can spend many years in low-paid work under conscription. Asmara says an ongoing threat from Ethiopia makes extended national service essential.
Eritrea's "critics will argue that it is trying to divert international attention away from the alleged crimes against humanity, and justifying its need for an enormous military and compulsory conscription," King said in a brief commentary.
Eritrea, which is under UN sanctions, says world powers have failed to push Ethiopia to accept an international arbitration ruling demarcating the boundary. Ethiopia's government has said it wants talks on implementation.
Eritrea and Ethiopia routinely accuse each other of backing rebels trying to destabilize and topple the other's government, a legacy from the two-year war.
