Meles Zenawi was interviewed by the BBC in 2008. Photo : bbc.com

Mr Meles took power as the leader of rebels that ousted communist leader Mengistu Haile Mariam in 1991 and led the country's economic transformation.

He was austere and hardworking, with a discipline forged from years spent in the guerrilla movement - and almost never smiled, says Elizabeth Blunt, the BBC's former correspondent in Addis Ababa.

Liberian President Ellen Johnson Sirleaf said Mr Meles was an "intellectual leader for the continent", and the UK Prime Minister David Cameron called him "an inspirational spokesman for Africa" who had lifted millions out of poverty.

But a spokesman for al-Shabab Islamist militants in Somalia - where Mr Meles twice sent troops to fight - told Reuters news agency they were "very glad" of his death, saying Ethiopia was "sure to collapse".

'Sudden infection'
Ethiopia's Council of Ministers announced "with great sadness the untimely death of Prime Minister Meles Zenawi" in a statement, state TV reported.

"The premier [had] been receiving medical treatment abroad for the past two months and his health was improving, but due to a sudden infection which occurred [on Sunday], he went back to hospital for emergency treatment, and even if a lot of medical attention was given by his doctors, he died yesterday [Monday] at around 23:40," the statement said.

Mr 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.

Some reports suggested Mr Meles was in hospital in Belgium, suffering from a stomach complaint. Other reports said he was in Germany.

Deputy Prime Minister Hailemariam Desalegn, who is also Ethiopia's foreign minister, will become acting head of government.

A period of mourning had been declared until the funeral, government spokesman Bereket Simon told reporters. No timing has been announced.

Mr Bereket said the prime minister had struggled with illness for a year, but he had continued to work regardless.

Mr Bereket insisted Ethiopia was stable and "everything will continue as charted" by the late prime minister.

This theme was echoed by state television, which stated that "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".

It broadcast footage of Mr Meles accompanied by solemn instrumental music.

Three weeks ago, spokesman Mr Bereket dismissed reports Mr Meles was critically ill, and declined to give any details about Mr Meles' whereabouts.

'Devil incarnate'
Ethiopia's economy has grown rapidly in recent years, despite the secession of Eritrea and the subsequent war between the two countries.

Under Mr Meles, Ethiopia became a staunch US ally, receiving hundreds of millions of dollars in aid over the years, and hosting the US military drones that patrol East Africa.

He won accolades from the West for sending troops to battle Islamist militants in Somalia, says the BBC's James Copnall.

But concern had been growing about the lack of democracy and human rights in Ethiopia, our correspondent in the region says.

At least 200 people died in the violence that followed the 2005 elections, and many journalists and politicians have been locked up.

One rights critic, Commander Assefa Seifu, called Mr Meles "a devil incarnate".

"He was always talking about democracy, civil rights, adherence to [the] constitution and the like. But it was only a lip service," he told the BBC.