(Recasts with preliminary results)

By Paul Simao

LUANDA, Sept 6 (Reuters) - Preliminary results from Angola's parliamentary election show the ruling MPLA headed for a landslide victory over its opponents, the African nation's electoral commission said late on Saturday.

The MPLA, which has ruled the former Portuguese colony since independence in 1975, received more than 81 percent of the vote at the national level, the commission announced at a midnight news conference.

UNITA, the largest opposition party, was winning just over 10 percent. The results were based on 35 percent of the votes cast in the two-day poll, which UNITA and other opposition parties have condemned as illegitimate.

The MPLA also was seen crushing the opposition at the provincial level.

Angola's parliamentary elections use a variation of proportional representation, with seats allocated based on results from the national and provincial levels.

"We want to stress that these are provisional results," Adao de Almeida, a commission spokesman, told reporters at the press conference in the capital Luanda. He said the next round of results would be released on Sunday morning.

Officials have 15 days to release the full results.

UNITA CHALLENGE

The MPLA had been widely expected to win the election, but the current numbers suggested the party was within reach of the coveted two-thirds majority that would allow it to make sweeping changes to the country's constitution.

The MPLA held 129 of the 220 seats in parliament heading into the election, with the remainder controlled by UNITA and a handful of smaller parties.

The results came several hours after polls closed. Voting began on Friday but was extended into Saturday because of delays and confusion at polling stations in Luanda province, home to 21 percent of Angola's 8.3 million registered voters

UNITA has vowed to challenge the legality of the poll in the Constitutional Court.

"We have no choice but to file the challenge. Conditions did not exist for the election in Luanda (province) yesterday and they still do not exist today," UNITA spokesman Adalberto da Costa told Reuters.

The government has denied any electoral wrongdoing, while admitting that there had been administrative glitches in some areas, particularly around Luanda. MPLA spokesman Norberto dos Santos said UNITA's legal battle was without merit.

A disputed poll could shatter the fragile political stability that has existed in the oil-rich nation since the end of a 27-year civil war in 2002. (Editing by Charles Dick)

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