Ethiopian Prime Minister Meles Zenawi dies at the age of 57, state media says. State television in Ethiopia said he died after contracting a sudden infection.
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Meles died in a hospital abroad, said state media and a government spokesman, but they did not say exactly where or give details of his ailment.
Speculation about his health mounted, including rumours of cancer, when he missed an African Union summit in Addis Ababa last month.
Meles took power as the leader of rebels that ousted communist leader Mengistu Haile Mariam in 1991.
He had dominated Ethiopian public life since the 1990s, as president and then prime minister.
"Prime Minister Meles Zenawi passed away yesterday (Monday) evening at around midnight," government spokesman Bereket Simon said, adding that he was "abroad" when he died, according to AFP news agency.
"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."
Some opposition media have said that Meles died in July.
Read Jon Snow's blog: Zenawi's death spells out Africa's conundrum
State television said he had died after contracting a "sudden" infection.
Deputy Prime Minister Hailemariam Desalegn, who is also Ethiopia's foreign minister, will be acting head of government, state television said.
"Even if Ethiopia has been badly affected for missing its great leader, Prime Minister Meles Zenawi initiated fundamental policies and strategies which will be further strengthened," the TV said.
Meles had not been seen in public for some eight weeks prior to his death, and was reported to have been admitted to hospital in July.
At the time he declined to give any details about Meles's whereabouts or what he was suffering from.
But reports suggested Meles was in hospital in Belgium, suffering from a stomach complaint.
Meles was considered a leader that the west could count on in its fight against al Qaeda-linked groups and he twice sent troops into neighbouring Somalia to help crush rebellions.
He was also widely credited for steering one of the world's poorest countries to sustained high economic growth but he cracked down hard on dissent and his image abroad was tainted after he jailed opposition leaders following the disputed 2005 election.
In an interview with Channel 4 News in January 2007 he said he accepted that the "post-election trauma" had tarnished the reputation of Ethiopia overseas.
Meles told Jon Snow that lessons had been learned, despite international human rights organisations reporting that little had improved in this area.
He defended his government against the organisations' accusations pointing out that Ethiopia is an emerging democracy. "This is a work in progress and therefore it has its own imperfections."
More recently, opponents and journalists have been arrested under a 2009 anti-terrorism law.
"Today is a day of joy for most Ethiopians and all freedom loving people around the world," opposition website Ethiopian Review said, describing Meles as a "genocidal tyrant".
At the time of the crackdown on journalists, Live Aid organiser Bob Geldof, who sat with Meles on the Commission for Africa, was vociferous in his condemnation of the Ethiopian government's actions.
"They make me puke," he told Channel 4 News.
"Meles Zanawi is a very seriously clever man... What is he doing? What is he doing closing down radio and journalists and that. It's a disgrace."