Ivory Coast: Reports of massacre by forces loyal to Outtara as they take Abidjan (VIDEO)

French peacekeepers in Ivory Coast have taken control of the airport in the main city of Abidjan, after aid agencies said at least 800 people were killed in a massacre outside the city.

Forces loyal to president-elect Alassane Ouattara, meanwhile, now control more than 90 percent of Abidjan, having taken over the capital, Yamoussoukro, in the past three days.

According to the International Committee of the Red Cross, the massacre took place late Saturday in the wake of a fierce battle for the town of Duekoue in the west as Ouattara's troops moved toward Abidjan to try to oust incumbent leader Laurent Gbagbo.

''It's truly horrific. We don't have any information about the authors of these killings,'' Red Cross spokesman Kelnor Panglung said.

An ICRC spokeswoman in Geneva, Dorothea Krimitsas, said: "There is no doubt that something on a large scale took place in this city, on which the ICRC is continuing to gather information,"  adding that Red Cross workers had "themselves seen a very large number of bodies".

U.N. Secretary General Ban Ki-moon has demanded that Ouattara take action against any of his followers who took part in a massacre, according to the Australian Broadcasting Corporation.

U.N. spokesman Martin Nesirky said: "The secretary-general expressed particular concern and alarm about reports that pro-Ouattara forces may have killed many civilians in the town of Duekoue in the west of the country. The secretary-general said those responsible should be held accountable.

But Ouattara reportedly denied to Ban in a telephone conversation that his followers were involved in the events in Duekoue and said he had ordered an investigation into the unrest.

The U.N., the U.S. and the African Union are calling on Gbagbo, 65, to hand power over to Mr Ouattara, 69, whom they recognize as the winner of the nation's presidential election last November.

Gbagbo refuses to accept defeat and, having seized the country's main television station, reportedly issued a final call to arms Saturday when a disheveled TV announcer addressed the nation saying Gbagbo was at his residence and that it had not been attacked. Soldiers could be seen on the set calling on police, military, customs officers, coast guard and forest rangers to report for duty to protect Gbagbo.

Meanwhile, France sent 300 troops to join the U.N. mission in Ivory Coast overnight, the French Ministry of Defense said Sunday, CNN reported. There were about 7,500 foreign troops already in the country under the U.N. mandate.

U.N. helicopters patrolled the skies over the city Sunday, according to a resident.