Angolan President Jose Eduardo dos Santos, who has been in power since 1979 and is one of Africa's longest-ruling leaders, said on Friday he intended to step down in 2018 but gave no reason for his decision and did not name a preferred successor.
Angola, a member of OPEC and Africa's second largest oil exporter after Nigeria, has been hit hard by the slump in global crude prices. Oil export revenues account for more than 90 percent of foreign exchange revenues.
"I took the decision to leave active political activity in 2018," Dos Santos, 73, said in a speech to members of his ruling MPLA party's key decision-making organ that was broadcast on radio without elaborating. He did not elaborate.
Angola, a former Portuguese colony, holds its next parliamentary election in 2017 and the leader of the winning party will then become president. MPLA leader Dos Santos was re-appointed to a new five-year term as Angola's president in August 2012 after his party scored a landslide win.
It was not immediately clear whether Dos Santos would retain his post as MPLA leader during the next election or take part in the campaign.
A year of weak oil prices has hammered Africa's third largest economy and the government is in discussions with the World Bank and International Monetary Fund about possible financial assistance.
Dos Santos' mild, inscrutable public demeanour belies his tight control over Angola, where he has overseen an oil-backed economic boom and the reconstruction of infrastructure devastated by a 27-year-long civil war that ended in 2002.
Critics accuse him of mismanaging Angola's oil wealth and making an elite, mainly his family and political allies, vastly rich in a country ranked amongst the world's most corrupt.
Dos Santos is Africa's second longest ruling leader after Equatorial Guinea's President Teodoro Obiang Nguema Mbasogo.
Vice-President Manuel Vicente - former head of state oil firm Sonangol - is seen as a likely successor to Dos Santos.
"(Dos Santos) has been grooming Vicente for quite a while now ... He has deputised for him on a number of important occasions, which sent a strong signal," said Gary van Staden, a Johannesburg-based political analyst with NKC African Economics.
But another analyst said the president was grooming his son, Jose Filomeno de Sousa dos Santos, to succeed him. The younger Dos Santos currently heads Angola's sovereign wealth fund.
"It may mean the succession is in progress and that it will be a dynastic one," said Nelson Bonavena, an economics lecturer at the Catholic University of Angola and political analyst.
Another Angola expert, Ricardo Soares de Oliveira of Britain's Oxford University, said the news of Dos Santos' planned exit should be treated cautiously.
"Dos Santos' departure from power has been the talk of the town in Luanda for 15 years. He has always hinted that he wanted to leave but this is the most specific commitment he has ever made," he said.
"The fact that he put a date to it is a powerful marker and would come back to haunt him if he were to renege on it."