* Pro-Gbagbo officials tear up results sheet
* President's party contests results in north
* Gunfire rings out in main city Abidjan
(Adds U.S. statement)
By David Lewis and Loucoumane Coulibaly
ABIDJAN, Nov 30 (Reuters) - Ivory Coast's opposition accused President Laurent Gbagbo on Tuesday of blocking the release of results from a tense vote because he knew he had lost, and Gbagbo supporters disrupted a reading at the poll commission.
The first batch of results from a run-off were due on Tuesday, but they were delayed in the morning and a news conference held in the evening to start announcing them was scuppered when pro-Gbagbo members of the election commission tore up results as the spokesman tried to read them out.
The election body has until Wednesday to announce a winner.
Gbagbo's party said it would formally challenge the run-off results in the rebel held north, where his rival Alassane Ouattara did well in the first round, because of intimidation by rebel New Forces soldiers of Gbagbo's supporters.
Sunday's vote was meant to end the process of reunifying the world's top cocoa grower, divided since a 2002-2003 civil war, but it has underlined the north-south divisions that caused it.
"The presidential camp is trying to prevent the proclamation of the results," Ouattara's campaign director Marcel Amon Tanoh told Reuters earlier in the day.
"If Mr Laurent Gbagbo knew he'd won, he wouldn't have ... prevented the CEI (commission) from speaking on the radio and TV ... Gbagbo knows he's lost."
Representatives of Gbagbo's campaign were not available to respond to the accusation.
U.S. Secretary of State Hillary Clinton called on "Ivorian leaders to act in a responsible and peaceful manner."
"We strongly urge candidates to allow the counting and announcement of the results to take place without interference and to respect the results that are announced," she said.
Two pro-Gbagbo members of the election commission accused the body's spokesman, who tried to read results to journalists, of "an electoral hold-up" before tearing up a sheet of results.
One shouted that the results had not yet been consolidated so could not be read out.
Bursts of gunfire rang out in central Abidjan on Tuesday evening but it was not clear who fired the shots.
Earlier in the day, security forces were deployed around the election commission's Abidjan office, which was blocked off with a barrier. Journalists who had been waiting for results inside the building were told to leave, witnesses said.
The United Nations has said the poll had been democratic despite some irregularities, intimidation and violence, and the African Union urged candidates to accept the results.
International observers, including the European Union, have all noted violence and irregularities but said it was too early to know if it would alter the result.
"Both sides have been prone to provocative claims against the other and should base any election complaints on evidence," the Carter Center observer mission said, calling on the election commission to stem the spread of rumours by announcing results.
Several cocoa exporters said they had shut down operations. Farmers last week rushed through deliveries in advance of the vote, and supplies this week were expected to be scant.
"There is no point in staying open because yesterday there were no deliveries and there are none expected for this week," said one exporter, who asked not to be named."
March cocoa futures in London ended up 40 pounds or 2.7 percent at 1,895 pounds a tonne.
On Monday, Gbagbo called for results from three northern regions to be cancelled, alleging intimidation by the New Forces rebels, whom he has accused of backing Ouattara.
The rebels have denied the charge. Ouattara's camp has also complained about the election in Gbagbo's stronghold in the west, but has not said it will mount a challenge.
A Western diplomat who is following the process said U.N. mission chief Y.J. Choi's endorsement of the vote on Monday was significant. "Any party that wants to challenge the results will have to challenge this analysis. This was an important message."
Observers said turnout was 65-70 percent, down from more than 80 percent in the first round. (Additional reporting by Loucoumane Coulibaly; Writing by Tim Cocks and David Lewis)