Meles Zenawi, Ethiopia’s long-time ruler and a major U.S. counter-terrorism ally who is credited with economic gains but blamed for human rights abuses, died of an undisclosed illness after not being seen in his East African country for weeks, Ethiopian authorities said Tuesday. He was 57.

Meles died in a Belgian hospital Monday just before midnight after contracting an infection, authorities said.

Hailemariam Desalegn, who was appointed deputy prime minister and minister of foreign affairs in 2010, became acting prime minister and will be sworn in as prime minister after an emergency meeting of parliament, said Bereket Simon, the communications minister. Parliament is controlled by Meles’ ruling party and governing coalition, ensuring Hailemariam will be approved. No new elections will be scheduled, Bereket said.

Under Meles, Ethiopia saw strong gains in the education sector with the construction of new schools and universities. Women gained more rights. And in the mid-2000s, Ethiopia saw strong economic growth, which won Meles international praise. The International Monetary Fund in 2008 said Ethiopia’s economy had grown faster than any non-oil exporting country in sub-Saharan Africa.

On the downside, human rights groups have long denounced Meles’ government for its use of arbitrary detention, torture, and surveillance of opposition members. The ONLF, an opposition group that mostly consists of ethnic Somalis, has openly clashed with the government, including in 2007 when Ethiopia sent troops to Somalia to fight al-Shabab militants.

Meles was the third African leader to die in office this year, following deaths in Malawi and Ghana. He is survived by his wife, Azeb Mesfin, a member of parliament, with whom he had three children.