Meles Zenawi, the influential prime minister of Ethiopia, died Monday at the age of 57 of an undisclosed illness after weeks of speculation about his health, the Ethiopian state television announced Tuesday.

"Prime Minister Zenawi suddenly passed away last night. Meles was recovering in a hospital overseas for the past two months but died of a sudden infection at 11:40," the state television said. He died from a sudden infection while recovering from an illness of unspecified nature, wire agencies reported citing the state media.

Deputy Prime Minister Hailemariam Desalegn has taken charge as the acting prime minister.

Meles was admitted to a hospital abroad in July, Reuters reported. His health became a focus of speculation after he failed to attend an African Union summit in the capital Addis Adaba in mid-July. Diplomats in Addis Ababa had earlier stated he was being treated in Brussels while others said he was in Germany.

Meles, who became Ethiopia's president in 1991 and prime minister in 1995, was regarded a major regional security partner of the United States. Ethiopia has been a U.S. security base for military patrol over neighboring Somalia.

Meles and the members of the Transitional Government of Ethiopia (TGE), established in July 1991, pledged to oversee the formation of a multi-party democracy. The election for a 547-member constituent assembly was held in June 1994. The assembly adopted the constitution of the Federal Democratic Republic of Ethiopia in December 1994.

Ethiopia's first democratic elections for the national parliament and regional legislatures were held in 1995. Most opposition parties chose to boycott these elections, ensuring a landslide victory for the Ethiopian People's Revolutionary Democratic Front (EPRDF) which formed a government headed by Meles.

The early years of governance under Meles are widely regarded to have promoted a policy of ethnic federalism, devolving significant powers to regional, ethnically-based authorities in Ethiopia.

In 2010, however, observers declared that the Ethiopian parliamentary elections failed to comply with international standards saying that the EPRDF used the advantage of incumbency to restrict political space for opposition candidates and activists.

Meles won another five-year term in office after reportedly receiving 99 percent of the vote.

He came under fire again in 2011 when the Ethiopian government arrested more than 100 activists, journalists and political leaders for alleged involvement in terrorist activities and charged many of them under Ethiopia's controversial anti-terrorism proclamation passed in 2009. Five journalists and two opposition members are convicted on terrorism-related charges while several others are currently on trial.

The Human Rights Watch (HRW) wrote an open letter to President Barack Obama in May expressing concern over Washington inviting Meles to attend a meeting on food security during the G8 summit in Camp David.

"After more than two decades of Meles Zenawi's leadership, Ethiopia's institutions have become mere extensions of ruling party power," HRW wrote.  "The country has steadily grown more authoritarian since the 2005 elections ended in bloodshed and controversy. The ruling party won more than 99 per cent of the seats in both the 2008 local government elections and the 2010 general parliamentary elections, mainly due to the government's comprehensive crackdown on dissent."

"The United States, the World Bank, and other states and institutions have shown little or no attention to Ethiopia's worsening human rights record," the letter noted.

"By inviting Prime Minister Meles to the G8 summit, the U.S government is sending a message that at best shows a lack of concern about the human rights situation in Ethiopia, and at worst, will be perceived as a U.S. endorsement of the Ethiopian government's policies."

Despite his tainted human rights record, Meles was regarded by the Western observers as having played an irrefutable role in Ethiopia's progress.

A leaked 2009 U.S. diplomatic cable described Meles as "quiet, deliberative and certainly not a 'man about town,'" adding he was a "voracious reader and very introspective," reported al Jazeera.

Meles oversaw the independence of Eritrea from Ethiopia in 1993, but later resorted to a border war in the period between 1998 and 2000 that led to tens of thousands of casualties.

Meles also invaded Somalia in 2006, but withdrew his forces due to increased guerilla resistance only to attack the country again in 2011.