LUANDA - The party that has ruled Angola continuously for nearly 50 years claimed victory on Friday in this week's election, after the electoral commission put its share of the vote at 51%, but the leader of the main opposition coalition rejected the results.

Fewer than half of Angola's registered voters turned out for Wednesday's election, which now looks certain to give President Joao Lourenco a second five-year term and extend the rule of the MPLA, which has governed the southern African oil producer since independence from Portugal in 1975.

With more than 97% of the vote counted, the election commission said on Thursday the formerly Marxist People's Movement for the Liberation of Angola, or MPLA, was ahead with a 51% majority while its longtime opponent, the National Union for the Total Independence of Angola, or UNITA, had 44.5%.

"We have reached yet another outright majority. We have a calm majority to govern without any kind of problem and we will do it," MPLA spokesman Rui Falcao told a news conference in the capital Luanda, a city that overwhelmingly voted for UNITA.

However, UNITA leader Costa Junior, addressing journalists and supporters for the first time since the vote, rejected what he called "brutal" discrepancies between the commission's count and their own tally.

"There is not the slightest doubt that the MPLA did not win the elections," he said. "UNITA does not recognise the provisional results."

It was Angola's most closely fought poll yet, with unprecedented gains for the opposition in parliamentary seats.

Analysts fear any dispute could ignite violence among a poor and frustrated youth who voted for Junior. The MPLA and UNITA, formerly both anti-colonial guerrilla groups, were on opposing sides of an on-off civil war after independence that lasted 27 years until 2002.

Junior urged Angolans to keep calm, which so far they mostly have, aside from the odd protest broken up by tear gas and baton-wielding police.

Civil society activists shared images on social media of dozens of young people marching, chanting and waving banners in protest against electoral fraud in the coastal town of Lobito on Friday. Reuters was unable to verify these images.

Junior must lodge a complaint to the commission, and if it is rejected, he can challenge the result in the Constitutional Court, which must rule on the matter within 72 hours.

LOW TURNOUT

If the results tally stays as it is then UNITA, for the first time, will have deprived the MPLA of the two-thirds majority needed to pass major reforms - the ruling party will instead need the backing of other lawmakers.

But perhaps even more telling was how few voters showed up to choose between two political entities which have dominated Angolan politics since independence. Election data released on Friday showed that turnout was 45.65% of eligible voters.

Lourenço, 68, has pledged to extend reforms in his second term, including privatising poorly-run state assets. But many Angolans still live in poverty despite promises of a fairer distribution of wealth in Africa's second biggest oil producer - a fact which benefited UNITA, popular with poor, jobless youths.

UNITA posted an image of Junior on its official Instagram account with the caption: "The President", while the MPLA posted a video of Lourenço on social media thanking Angolans for the outcome.

As she watched the news on her phone, 47-year-old Antonia Neto, who works at a coffee shop at Luanda airport, said she was not happy with the results, but she remained hopeful.

"There is a lot of discontent," she said. "Maybe things will be better in the next election."

The United States called for patience as the vote tally continues.

"The United States congratulates the people of Angola for making their voices heard in Wednesday's elections. We continue to observe the electoral process as votes are counted. We encourage peace and patience as the vote tally process continues," White House spokesperson Karine Jean-Pierre said.

(Reporting by Catarina Demony Additional reporting by Sergio Goncalves in Lisbon Writing by Francesco Guarascio and Tim Cocks Editing by Mark Heinrich, Kirsten Donovan)