Around 200 UN staff are evacuating their base in Ivory Coast after coming under sustained attacks from forces loyal to president Laurent Gbagbo.

The employees were flown by helicopter from their headquarters in Abidjan to the city's airport, the Associated Press reported. Another helicopter will take them to the northern city of Bouake.

The evacuation order is for all "essential employees." Nonessential employees were already evacuated several months ago. The UN has about 12,000 peacekeepers in the war-torn west African country.

On Saturday, four UN soldiers were seriously wounded when pro-Gbagbo special forces fired a rocket-propelled grenade at a UN armoured personnel carrier.

In Paris, the French defence ministry said French troops have taken over Abidjan's airport and that France plans to send an additional 300 soldiers to Ivory Coast.

Gbagbo's state TV accused the French troops of preparing a genocide like that in Rwanda in 1994 in which more than 800,000 people were killed.

A caption on state TV read: "[French president Nicolas] Sarkozy's men are preparing a Rwandan genocide in Ivory Coast. Ivorians, let us go out en masse and occupy the streets. Let us stay standing."

Sarkozy called a cabinet meeting for Sunday afternoon to discuss the growing crisis. More than 1,500 foreigners – including about 700 French nationals and 600 Lebanese – are sheltering in a French army camp.

After a day and night of intense fighting, Abidjan was calm on Sunday morning with sporadic gunfire, Reuters reporters and residents said. Heavy canon fire and shooting were heard overnight in the pro-Gbagbo neighbourhood of Yopougon and also in Cocody.

Gbagbo's government had urged civilians to form a human shield around his office and home. Hundreds of young men gathered near the palace on Sunday morning.

But an adviser to Alassane Ouattara, winner of last November's presidential election, claimed fighters are preparing for a final push to depose Gbagbo. The adviser, who did not wish to be named, said pro-Ouattara forces gathered outside the Abidjan late on Saturday and planned to advance on Sunday.

Meanwhile, Ouattara has clashed with the UN over claims that his forces were involved in a massacre of hundreds of civilians – an allegation that threatens to tarnish his credentials as the democratically elected, internationally supported leader.

The UN mission (ONUCI) said traditional hunters known as Dozos fought alongside Ouattara's forces and took part in killing 330 people in the western town of Duekoue.

The International Committee of the Red Cross said that at least 800 people were killed in intercommunal violence in Duekoue last week. It is not clear whether the 330 counted by the UN is included in that figure.

Guillaume Ngefa, deputy head of the human rights division of the UN mission in Ivory Coast, blamed 220 of the deaths on pro-Ouattara forces. He told France24 television the killings happened between Monday and Wednesday as pro-Ouattara troops advanced southward. Pro-Gbagbo militia fighters killed more than 110, he added.

The UN said secretary general Ban Ki-moon spoke late on Saturday with Ouattara, who told him his forces were not involved in the Duekoue killings.

Ouattara's camp hit back and blamed the UN. His justice minister Jeannot Ahoussou-Kouadio accused the nearly 1,000 peacekeepers based in Duekoue of abandoning the town and leaving civilians at the mercy of vengeful Gbagbo fighters.

"The government notes that the (UN mission) retreated from the town of Duekoue before its liberation by the Republican Forces [rebels] at the same time that the town was prey to looting and exactions of every type being committed by the militia and mercenaries of Mr Laurent Gbagbo," he said.

The UN mission said most of its soldiers were deployed around a Catholic mission, protecting some 15,000 people who had sought refuge there. Aid organisations say atrocities that could qualify as war crimes and crimes against humanity are being committed by both sides.

After swiftly taking control of swathes of the country, pro-Ouattara forces have met fierce resistance in Abidjan over the past three days. Troops loyal to Gbagbo have held on to positions around the presidential palace, Gbagbo's residence and the state television.

The fighting has brought the number of people killed since the post-election violence began in November to more than 1,300.

Hillary Clinton, the US secretary of state, said: "We are deeply concerned by the dangerous and deteriorating situation in Cote d'Ivoire, including recent reports of gross human rights abuses and potential massacres in the west. The United States calls on former President Laurent Gbagbo to step down immediately."

She added: "We also call on the forces of president Ouattara to respect the rules of war and stop attacks on civilians. President Ouattara's troops must live up to the ideals and vision articulated by their elected leader."