U.N. Secretary-General Ban Ki-moon is urging Ethiopia and Eritrea "to exercise maximum restraint" following clashes on their disputed border.

Eritrea accused Ethiopia of "military aggression" by attacking its positions in a border area that saw one of the bloodiest battles during their 1998-2000 border war. Ethiopia's military said its troops were provoked into launching a counter-offensive after Eritrean forces fired into Ethiopian positions on Sunday.

Ban met Ethiopian Prime Minister Hailemariam Desalegn in Brussels on Wednesday and Deputy Secretary-General Jan Eliasson phoned Eritrean Foreign Minister Osman Saleh Mohammed to urge restraint "and refrain from any act or statement that could exacerbate the situation," the U.N. said.

Eritrea and Ethiopia have feuded over their border since Eritrea gained independence from the Addis Ababa government in 1993 after a 30-year guerrilla war.