"Prime Minister Meles Zenawi passed away yesterday evening at around midnight," Bereket Simon said, adding that the 57-year-old "was abroad" when he died, without giving further details.

Meles had not been seen in public for two months, and had been reported to have been sick in a hospital in Brussels, although Bereket gave no details of the illness.

"He had been recuperating well, but suddenly something happened and he had to be rushed to the ICU (intensive care unit) and they couldn't keep him alive."

According to Ethiopia's constitution, Deputy Prime Minister Hailemariam Desalegn is to "act on behalf of the Prime Minister in his absence".

Diplomats and analysts in Addis Ababa say it has not been clear how the government has been run since Meles was reported to have fallen sick in June.

The position of president is largely honorific and Meles, a former rebel fighter who came to power in 1991 after toppling the bloody dictatorship of Mengistu Haile Mariam, held the real political power.

On paper Meles' government has fostered a policy of ethnic federalism, devolving significant powers to regional, ethnically-based authorities but central control remains firmly in the hands of the ruling party.