The government held a news conference last month and announced Meles received treatment for an unspecified illness.
His absence was more evident last month when Ethiopia hosted an African Union summit in its capital of Addis Ababa. Meles, a key player in talks on the tensions between Sudan and its rival neighbor South Sudan, did not attend.
Former U.N. Secretary-General Kofi Annan said Ethiopia under Meles had "played a key role in both the region and the African continent."
"I hope that his successor will continue to be a driving force on a wide range of issues, from brokering peace negotiations to shaping development relationships," Annan said.
Ethiopia, a key Western ally often lauded for effective use of aid money, is surrounded by unstable nations such as Somalia and Sudan. Meles has been credited with working toward peace and security in the region, and the Ethiopian army sent peacekeepers to battle the Islamic extremist group Al-Shabaab in Somalia.