ABIDJAN (Reuters) - Ivory Coast's rebels say they have suspended participation in the power-sharing government in protest at the killing of opposition demonstrators in the main city of Abidjan.

"We have suspended our participation in the government ... because the security forces have been shooting in Abidjan," Guillaume Soro, political leader of the rebel movement, told Reuters by phone from the rebel stronghold of Bouake.

At least seven people died in clashes between protesters and security forces in Abidjan on Thursday as marchers gathered for a banned protest against President Laurent Gbagbo by an alliance of the two main opposition parties and the rebels.

The rebels and several opposition parties joined the government after a French-brokered peace deal was signed in January last year to end civil war in the world's biggest cocoa grower.

But the rebels, who now call themselves the New Forces and still control the northern half of the country, have accused Gbagbo of stalling on agreed reforms.

Soro said anti-government protesters in Bouake were asking the rebels to let them march into government-held territory following the shootings in Abidjan.

Army spokesman N'Goran Aka said two policemen had died from gunshot wounds and three had been injured in a clash with demonstrators in the Abidjan suburb of Abobo in which a passerby also died.

Two marchers had died in a suburb called Koumassi, he said, while a policeman told Reuters in a third area known as Yopougon that the security forces had shot dead two protesters there.

Tension has been building in the sprawling port city all week as march organisers pledged to press ahead with their protest despite the risk of a showdown with the army.

MARCH CALLED OFF

An opposition politician and spokesman for the protesters later called off the march, branding the West African country's leadership a "dictatorship" and saying about 20 marchers had been shot dead by the security forces.

"I have called on our militants to return home because we are not protesting to make war," said Alphonse Djedje Mady, secretary-general of the opposition Democratic Party (PDCI).

"My feelings are of grief and sadness. The army fired on a peaceful demonstration, on people with nothing in their hands. That can only resemble a dictatorship," he told Reuters.

MI-24 helicopter gunships clattered overhead as small groups gathered in different parts of the city earlier in the day. Tear gas fired by groups of paramilitary and anti-riot police mixed with the smoke from tyres burning in near-empty streets.

"The defence and security forces will not tolerate chaos. They are ready to destroy any attack from wherever it comes," Aka told state radio.

Gbagbo's opponents are demanding the full implementation of a French-brokered peace deal signed last year to end the civil war, in which thousands died and more than a million were forced from their homes.

The war officially ended in July but the opposition accuses the president of stalling on agreed reforms. Gbagbo's supporters say the rebels and their political allies are criminals bent on taking power illegally.

U.N. Secretary-General Kofi Annan said on Wednesday he was deeply concerned about the deteriorating situation in Ivory Coast and called on all parties to "exercise utmost restraint".

Some 6,000 peacekeepers are due to deploy in the former French colony to help 4,000 French soldiers and about 1,000 West African troops keep the peace and disarm the combatants.