YAOUNDE (AFP) - As early results in Cameroon's presidential poll suggested that incumbent Paul Biya was heading for a fifth term in office opposition parties called for the vote to be ruled void because of rampant fraud.
But a delegation of former US congressmen said that the vote had been fair even if there remained room for improvement in the electoral process.
"The Social Democratic Front will ask the constitutional court to annul this election... which was very badly organized and resulted in massive fraud," Secretary-General Michel Tazoacha Asongany of the Anglophone party, one of the two main groupings, said.
The presidential candidate of a separate coalition of opposition parties, Adamou Ndam Njoya, called the vote "a masquerade, with overt fraud throughout the country."
"We are in the process of gathering information to bring this affair before the courts, in the hope that the judiciary will do its job," Ndam Njoya said.
The government's communications minister refused to comment on the charges, referring AFP to a news conference to be held by the minister with responsibility for the elections, Marafa Hamidou Yaya, at 5:00 pm (1600GMT).
On Monday night an hour after the polls closed Yaya said he had not heard of any incident of a kind to "call into question the fairness, transparency and freedom" of the vote.
Monday's vote was "fair", a team of US observers made up of former members of the US Congress said Tuesday, but the electoral process needed improvement.
The elections were conducted fairly," Greg Laughlin, head of the US Association for Former Members of Congress, told reporters.
"At the closing of the poll, we have never seen such a transparent way to show who got the vote. Every one was able to witness the process."
"While waiting for our report, which will be published on our web site, we can just say what we saw and it's quite positive for democracy in Cameroon."
Another delegation member said there was room for improvement "but in general, the process was free. This is what democracy is about."
However the SDF's Asongany insisted: "There were numerous irregularities both before the election and on voting day."
"In some polling stations, our members noted that at around 4:00 pm Monday, members of the RDPC (Biya's Democratic Rally of the Cameroonian People) were given voter cards that had not been used, and they voted," he said.
Ndam Njoya said that voters were ferried into polling stations in the town of Garoua in the north, while "elsewhere, real voters were prevented from casting their ballots and observers from the UDC (his Cameroon Democratic Union party) were barred."
"Biya will be elected fraudulently," he charged.
Only 4.6 million of Cameroon's 16 million people were registered to vote, with many saying they saw no point in casting their ballot because Biya was bound to win.
The opposition also slammed Yaya's announcement late Monday of partial results showing Biya ahead in nine out of 10 provinces.
"The results announced by the minister were false," Ndam Njoya claimed.
"The trends of which the minister spoke smack of manipulation," the SDF said.
Officials said that more than 4,500 election observers -- 192 from abroad, sent by the Commonwealth and the International Francophone Organisation, and foreign embassies, with the remainder from Cameroon -- were deployed around the country, which is slightly larger than the western US state of California.
Various irregularities were reported to AFP during the day. In some polling stations representatives of the different political parties were not present; some voters had not received their voting cards; others were not listed as registered to vote.