LUANDA - Angola's ruling MPLA headed on Sunday for a landslide victory in a parliamentary election which opposition parties have branded illegitimate, preliminary results showed.

The MPLA, which has ruled the oil-rich African nation since independence from Portugal in 1975, has taken almost 82 percent of the vote at the national level, the electoral commission announced.

The African country's main opposition party UNITA, a former rebel group, was far behind.

The ruling party was also seen crushing the opposition at the provincial level on the basis of about 50 percent of the votes after the two-day poll.

Angola's government has touted the ballot as a showcase for its recovery from civil war after flawed polls elsewhere in Africa and hopes that it will spur foreign investment. Angola rivals Nigeria as sub-Saharan Africa's biggest oil producer.

Although nobody is predicting a return to fighting, a disputed poll could shake the fragile political stability that has existed since the end of the 27-year war in 2002.

The electoral commission has stressed that results released so far are provisional.

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.

UNITA and other opposition parties say the vote should be held again.

GLITCHES

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.

Officials have 15 days to announce the full results of an election which has been keenly watched because of Angola's emergence as a major oil producer and the newest member of OPEC.

The MPLA had been widely expected to win the election, but the partial results 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.

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

Problems with voter registration lists have been cited as the main cause of the delays on Friday.

"The law was broken because the electoral registration was not distributed," Luisa Morgantini, who is leading a 120-member EU team, told Reuters. "We cannot say the process was done according to the rules."

Morgantini later said she was pleased with their efforts and impressed by the way in which Angolans had cast their votes.

An observer mission from the Southern African Development Community, a 15-nation group that includes Angola, said on Saturday the election was credible, free and transparent, according to Angola's state-run Angop news agency.

In the run-up to the poll, UNITA (National Union for the Total Independence of Angola) accused the MPLA (Popular Movement for the Liberation of Angola) of abusing state funds and state media. It also said its supporters had been harassed.

Independent Angolan election observers said on Saturday that the voting was largely free of violence and irregularities, but that it was too early to declare the poll legitimate.