ABIDJAN (AFP) - The French army took over Ivory Coast's main airport on Sunday as the battle for Abidjan dragged into a fourth day and recognised leader Alassane Ouattara came under fire for a massacre in the west.

In a telephone conversation with Ouattara, UN chief Ban Ki-moon demanded he take action against followers who took part in a massacre of about 800 people, a UN spokesman said Sunday.

Ouattara told Ban that his followers were not involved in events in the western town of Duekoue, spokesman Martin Nesirky said.

The international Red Cross and United Nations say about 800 people were killed in an operation by pro-Ouattara forces in the town last Tuesday as they took territory from Ivory Coast strongman Laurent Gbagbo.

Ouattara also told Ban he had ordered an investigation.

Gbagbo, meanwhile, resisting international calls to step down, mobilised his supporters around his strongholds in the seaside city.

The French force Licorne took control of the airport in Abidjan and Paris reinforced the troops with 300 men as over 1,500 foreigners sought refuge at the French military camp amid violence and looting in the city.

Early on Sunday residents and AFP journalists said Ouattara's fighters held firm to their positions as sporadic heavy arms fire broke out near the presidential palace. The whereabouts of Gbagbo were unknown.

As tension in the city, awaiting a final showdown, reached fever pitch, Gbagbo's state television broadcast virulently anti-French messages.

"A Rwandan genocide is being prepared in Ivory Coast by Sarkozy's men," read a ticker running across the screen, referring to French President Nicolas Sarkozy and the 1994 massacre of 800,000 in Rwanda in just three months.

"The French army has occupied the Felix Houphouet-Boigny airport, we are in danger," read another.

The RTI television station, a vital means of communication for Gbagbo to his loyalists, was briefly captured by pro-Ouattara fighters on Thursday night before Gbagbo troops regained control and restored the signal.

A message was played on Sunday in which Damana Pickas, a leader of the "Young Patriots", Gbagbo's most fervent backers, called for mobilization.

"It is the people's army. The army has become pure, the Republic has become pure," he said, after the defections to the rival camp.

"We need all the patriots, the resistance, to take to the streets. There are times when death is better than dishonour. But do not doubt our victory," he said.

Weary with failed diplomatic efforts to resolve a post-election crisis, Ouattara's army on Monday launched a lightning offensive across the country before arriving in Abidjan on Thursday.

Fierce attacks on Gbagbo's strongholds have shaken the city with artillery explosions and machine gun fire, but the strongman, internationally isolated, economically asphyxiated and virtually cornered in Abidjan, is fighting to the last.

All day Saturday RTI broadcast calls for mobilisation, urging civilians to form a "human shield" around Gbagbo's his residence. That evening hundreds of people including women and children were shown gathered in front of his home.

Reporters Without Borders said RTI was likely being transmitted from a mobile truck, which Ouattara's camp has promised "will be destroyed as soon as possible."

Meanwhile reports of carnage emerged in Duekoue where the International Red Cross said 800 died in one day in an incident "particularly shocking by its size and brutality".

The Catholic mission Caritas reported 1,000 were "killed or disappeared" while the UN mission gave an initial death toll of 330, saying while both camps were involved in the mass killings, the majority of deaths were caused by Ouattara fighters.

Ouattara's government accused "the loyal forces, mercenaries and militias of Laurent Gbagbo" of being behind mass graves discovered in the area.

The aid organization Medecins sans Frontieres on Sunday voiced alarm over the number of wounded people flooding into its medical centres in the west, saying medical supplies and medicine were running out and that the fighting was hampering access to the injured.

"There is real concern for some patients, who can practically no longer be treated in Ivory Coast," it said in a statement.

"The situation remains extremely tense and violent in and around several towns in the west of Ivory Coast," MSF said.

Between Tuesday and Saturday, 195 people with bullet or machete wounds had been treated by emergency services in Danane, Man and Bangolo, while MSF's mobile clinic teams were treating more than 500 patients a day, Renzo Fricke, in charge of emergencies at the non-governmental organisation, said.