By Tansa Musa
YAOUNDE (Reuters)- Cameroon's opposition parties said on Wednesday they would ask the Supreme Court to annul Sunday's presidential election because of what they called widespread irregularities.
The Commonwealth observer mission, in its preliminary findings, said the use of state resources in the campaign of incumbent Paul Biya's ruling CPDM party "challenged the notion of a level playing field".
Joshua Osih, vice-president of the main opposition Social Democratic Front (SDF), said evidence of double-voting and a lack of ballot papers in some polling stations meant the results, which are due in coming days, could not be credible.
"It is evident that this election will not give any winner any legitimacy. That is why we are filing a case with the Supreme Court for the election to be simply annulled," Osih told Reuters by telephone.
The election commission has up to two weeks from the vote to issue the validated results of the single-round election, which observers said passed off relatively peacefully.
Biya, in power in the central African state for 29 years, is widely expected to be re-elected in the poll, contested against over 20 rivals from the splintered opposition.
Biya, 78, acknowledged there may have been "imperfections" in the staging of the election, but denied fraud.
He was able to run for re-election only because he scrapped presidential term limits in 2008 -- a move which, added to street anger over food prices, provoked riots at the time in which more than 100 people died.
Albert Dzongang ran as candidate for the smaller opposition party Dynamique pour la Renaissance Nationale but was unable to vote because he could not get his voter card.
He told Reuters: "What happened on Sunday should simply be declared null and void."
Another opposition candidate, Anicet Ekane of the MANIDEM party, said his lawyers were also preparing to file a request with the Supreme Court for the vote to be annulled.
"LEVEL PLAYING FIELD?"
Election observers praised the peaceful conditions of the vote but raised concerns over the electoral process.
U.N. Secretary-General Ban Ki-moon urged parties to resolve any disputes through legal channels and called on the Cameroon authorities to ensure all claims were handled swiftly and transparently.
France, Cameroon's former colonial power, said the vote took place in "acceptable conditions", while the Commonwealth observer mission said in its preliminary report that the election met some basic democratic benchmarks.
However it noted limited public confidence in election body Elecam's handling of the election, problems with registration of voters, and the benefits Biya's ruling CPDM derived from the use of state resources such as ministry vehicles and the police force to help run its campaign.
"The magnitude of resources that appeared to us to have been deployed by the ruling CPDM party and its overwhelming advantage of incumbency challenged the notion of a level playing field in the entire process," it said in a written statement.
Cameroon's economy has considerable potential but has not grown as fast as expected in recent years.
The media and opposition have criticised Biya for lax governance, allowing corruption, red tape and nepotism to fester. Average income per head stands at an annual $2,000 -- higher than most of the region -- but the IMF has described its forecast 3.8 percent growth this year as below potential.
Oil output has fallen by two-thirds since the 1980s to about 66,000 barrels per day and development of the mining sector, which includes cobalt, nickel and manganese reserves, has been held back by inadequate electricity supplies.
Cameroon is the world's fifth largest cocoa producer and the region's breadbasket, supplying Chad, Central African Republic, Congo Republic and Gabon. It hosts the Chad-Cameroon pipeline.
Biya has said he will build roads, power plants and a deep sea port with the goal of securing emerging market status for Cameroon by 2035 -- putting it in the same bracket as countries such as Mexico and Malaysia.