Eritrea claims that Ethiopia has invaded its territory, Reuters reports. There is no response yet from Ethiopia.
Eritrea broke off from Ethiopia in 1991, though the two countries fought a war between 1998 and 2000 and tension remains high.
"The TPLF [Tigrayan People's Liberation Front] regime has today, Sunday 12 June 2016, unleashed an attack against Eritrea on the Tsorona Central Front," said teh Eritrean Information Ministry. "The purpose and ramifications of this attack are not clear."
The TPLF is one of the four parties in the Ethiopian government coalition.