By David Lewis and Jonny Hogg
KINSHASA (Reuters) - Four opposition challengers to Democratic Republic of Congo's President Joseph Kabila called on Tuesday for election results to be rejected, accusing authorities of systematic fraud.
Candidate Vital Kamerhe, a former government minister, said ballots had been marked ahead of the poll in favor of Kabila, and some voters prevented from entering polling stations during Monday's chaotic presidential and parliamentary elections.
Three other candidates also urged the Congolese not to accept any results from the vote, saying technical problems and fraud meant they would not be credible. However Kabila's top rival, Etienne Tshisekedi, did not join their call and his party said it was confident he would win.
"There can be no doubt as to the scale of the fraud, deliberately planned by those in power with the connivance of the national election commission," Kamerhe wrote in a letter to Kabila, the election commission and international bodies.
"Police chased witnesses from polling stations before counting could start," he said, citing reports by international observers and others that security forces took control of voting stations in Kinshasa.
"These elections must quite simply be annulled."
At least eight people have been killed in violence linked to Monday's elections, the second since the end of Congo's 1998-2003 civil war. Authorities went ahead with the polls despite international concerns about a lack of preparation.
"We have no faith in the results which will come out of these elections," presidential candidates Kengo wa Dondo, Antipas Mbusa Nyamwisi and Adam Bombole said in a statement.
Veteran opposition leader Tshisekedi did not join the calls for an annulment, and an official from his UDPS party said he was poised to win despite the irregularities.
"According to our estimations, Mr Kabila's fraud has not worked and we are ahead so we are not calling for a cancellation," UDPS secretary general Jacquemain Shabani said.
The national election commission has repeatedly denied accusations of bias and said it was confident that preparations for the election were largely in place.
Kabila, 40, has been widely viewed as the favorite in the single-round vote against 10 challengers. About 18,500 people are also running for 500 seats in parliament.
Some polling stations were burned down or attacked on Monday as frustrated Congolese tried to find out where they should vote or were prevented from doing so by a lack of voting equipment.
Election commission spokesman Matthieu Mpita said about 800 polling stations that either experienced problems during voting or did not open at all had either been allowed to vote on Tuesday or would finish the process on Wednesday.
But he said at least 130 polling stations in the southern Kasai provinces, which are opposition strongholds, would not see any extension to voting until enquiries had been carried out, adding that the trouble had been fomented by local politicians.
"We are going to give them a lesson," he said.
Anaclet Tshimbalanga, the president of TDH, a human rights group in West Kasai province, said at least 12 polling stations were torched in the provincial capital, Kananga, after residents said they found ballots already marked in favor of Kabila.
Mounoubai Madnodje, spokesman for the U.N. mission in Congo, said the United Nations was still delivering electoral materials on Tuesday to some areas which had yet to vote, including the central province of Bandundu.
"We've offered our helicopters to transport materials, so yes, we're still continuing to help," he said, adding the country was generally calm.
(Writing by Mark John; Editing by Janet Lawrence and Andrew Heavens)