Equatorial Guinea's main opposition party accused the country's regime of manipulating a referendum on a new constitution that would limit presidential term limits to two.
President Teodoro Obiang Nguema, Africa's longest-serving leader, backed the reforms that are seen as part of a charm offensive to clean up the image of his oil rich state, branded as one of Africa's most corrupt and autocratic.
But opposition leader Placido Mico, who previously dismissed the referendum as a sham, on Sunday pulled his agents out of polling stations, citing widespread irregularities and the intimidation of his supporters.
Preliminary results are expected tonight after some 1,500 polling stations across the country closed at 6:00 pm local time (1700 GMT).
FIRST SON
If the referendum is approved, the constitution would also be amended to create a vice presidential post, but critics speculate the job could be handed to Obiang's 41-year-old son, Teodoro Obiang Mangue.
The first son is reviled by many for his lavish lifestyle. He is best known for his love of sports cars and champagne and his $31-million home in Malibu, California.
The text of the proposed changes also does not make clear whether Obiang will have to step down when his term ends in 2016.
Mico said he withdrew all representatives from his Convergence for Social Democracy party from polling places at 1:30 pm (1230 GMT) after witnessing and hearing accounts of egregious election violations.
TORTURE THREAT CLAIMS
A young supporter of his party "was threatened with being tortured by a colonel" at a polling station in the capital Malabo, he said. Voters were facing pressure across the nation of 700,000, he added.
"There is no participation. It's not going beyond 25 percent. I have visited some 50 polling stations since 11:00 am. No one is voting" said Mico, the sole opposition lawmaker in the country's parliament.
Election officials had let unregistered people vote and voting was taking place in the open, rather than in isolated voting booths, he added.
"That is prohibited", he said.
DEMOCRATIC 'MILESTONE'
Information Minister Jeronimo Osa Osa Ecoro, said that voting had taken place in a "climate of calm, peace and tranquility".
Before polls closed he said that voting in his Anisok (northeast) constituency "for the moment is 99 percent in favour of reform" and called the vote a "democratic milestone".
Obiang, 69, is currently serving his fourth seven-year term since he seized power in a 1979 coup, usurping his notoriously ruthless and unhinged uncle Francisco Macias Nguema who was executed by firing squad.
He organised the referendum because he "wants his country, long ignored or despised, to acquire a diplomatic status that matches its new financial weight," said one diplomat, speaking on condition of anonymity.
The regime says the new constitution would also impose more checks and balances on the executive, improve the judicial system and ensure better protection of civic rights.
'LACK OFCONSULTATION'
But opposition leader Mico has decried a lack of consultation ahead of the vote.
"No one has seen the text, not the cabinet or any official body," he said. "We are submitting a text to a referendum that no one has seen. It's an invisible text."
In the mid-1990s oil was discovered in the little-known nation. Today, it is the continent's third sub-Saharan oil producer behind Nigeria and Angola.
Obiang has in part used oil revenues to bankroll a series of infrastructure projects, including those to accommodate the 2012 Orange Africa Cup of Nations football tournament, which Equatorial Guinea will co-host with neighbouring Gabon.
