ADDIS ABABA (Reuters) - Ethiopian Prime Minister Meles Zenawi, regarded by the West as a bulwark against Islamic militancy, died overnight in a Brussels hospital after a long battle with illness.
Speculation that Meles, 57, an ally of Washington who twice sent troops into neighbouring Somalia to help crush rebellions, was seriously ill had grown after he failed to attend an African Union summit last month.
Deputy Prime Minister Hailemariam Desalegn will be sworn in as acting prime minister by parliament and the ruling party will meet to choose a successor but no date has been set.
"The death of Prime Minister Meles has robbed Africa of one of its greatest sons," the African Union, which is headquartered in Addis Ababa, said in a statement.
Bereket Simon, Meles' right-hand-man and government spokesman, said the leader had been ill for a year and had passed away around midnight after he was suddenly rushed to intensive care.
Meles seized power in 1991 from Mengistu Haile Mariam's military junta and went on to become a towering political figure on the continent who was widely credited for steering one of the world's poorest countries to fast economic growth.
Rights groups criticised him for cracking down hard on dissent but the West generally turned a blind eye to the repression, reluctant to pick a fight with a partner in the fight against al Qaeda-linked groups in Africa.
British Prime Minister David Cameron said Meles was an "inspirational spokesman for Africa".
Cafes around Addis Ababa's affluent Bole Tele district were packed with people glued to television sets after a special news broadcast announced Meles' death.
The secretive government did not reveal where he was being treated or the nature of his illness but a European Union source said he died in Brussels where he had been a patient at the Saint-Luc University Hospital.
A cortege accompanied by police riders left a hotel next to the hospital, and took a casket, believed to hold Meles' body, to a private airstrip near the city's main airport.
Belgian military officials and police were at the airport as the casket was loaded onto an Ethiopian Airlines jet.
Somalia's al Shabaab militants, who encountered Ethiopian troops twice under Meles' tenure, once in 2006-2009 and again from December 2011, hailed the former leader's death.
"He led the African leaders who had fingers in Somalia for two decades, but all in vain," said spokesman Sheikh Ali Mohamud Rage.
Bereket said Africa's second most populous nation was stable and would continue on the path charted by Meles. The ruling party, Ethiopian People's Revolutionary Democratic Front, will select his permanent successor.
Negasso Gidada, a former president during Meles' tenure and now chairman of the opposition Unity for Democracy and Justice, said he hoped the transition of power would be peaceful.
"We urge the EPRDF to change for the good the political, democratic and human rights situation in the country," he said.
David Shinn, a former U.S. ambassador to Ethiopia, said he expected many of Meles' defence policies to remain the same.
"For internal security reasons, there will be a continuing focus on Somalia and I do not foresee any significant change towards Eritrea," said Shinn, referring to Ethiopia's arch-foe with whom it fought a decade-long border war.
Meles presided over a seven-year run of double digit economic growth, advocating a mix of heavy state spending and private investment.
He was widely applauded for ploughing money into infrastructure but criticised by some for selling off swathes of land to foreigners. Many Ethiopians complain that his close business ties with China did not translate into more jobs.
International rights groups criticised Meles' handling of dissent. He rounded up numerous opposition leaders after the disputed 2005 polls and several 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".
Former U.N. Secretary General Kofi Annan said Meles' death heralded a challenging time for Ethiopia.
"I ardently hope that the transition period will be smooth and peaceful and that Ethiopia sees leadership that reflects the aspirations of its people and realizes the potential of this extraordinary country," Annan said in a statement.
State television said details of Meles' state funeral would be announced soon.
Acting Prime Minister Hailemariam, 47, was an advisor to Meles in 2006 before being picked as his deputy in 2010, a surprise because of his relatively young age.
He had also replaced Meles as chair of a number of parliamentary committees in the past few years, a sign that he was being groomed for the post, diplomats say.
(Additional reporting by Feisal Omar in Mogadishu, Sebastian Moffat, Ethan Bilby and Ben Deighton in Brussels and Mohammed Abbas in London; Writing by Yara Bayoumy; Editing by Richard Lough and Anna Willard)