Rival fighters backing opposing presidential candidates in Ivory Coast were amassing in Abidjan, Ivory Coast's largest city, on Sunday, while French and United Nations peacekeepers took over the airport.

Speaking to CBC News on Sunday, Associated Press reporter Marco Chown Oved said UN tanks had joined the French presence to help secure the city — which is the country's financial capital — amid fierce skirmishes.

"It was sort of in response to the call from President Alassane Ouattara who wanted … the airport to be open to allow people who want to flee the fighting, if possible," Oved said, adding that the move was primarily a measure to protect civilians.

Most of the fighting is happening between ground forces.

"They do have tanks and mortars, but for the most part they are poorly dressed and poorly armed soldiers on the ground," he said. "This is going to be a fight that may go block to block, house to house."

The Department of Foreign Affairs warned Saturday that the 500 Canadians there should remain indoors with a supply of basic foods on hand and monitor the conflict closely. The department also advised against all travel to the country and has closed its embassy in Abidjan.

Clinton urges calm

Ouattara's victory in November's election was recognized first by the country's electoral commission, then by the UN and governments around the world.

World leaders including U.S. President Barack Obama and French President Nicolas Sarkozy have appealed to incumbent Laurent Gbagbo to step down, but he has refused to accept defeat. On Sunday, hundreds of pro-Gbagbo youth heeded his call to form a human shield around the presidential palace.

U.S. Secretary of State Hillary Clinton on Sunday called once again on Gbagbo to step down and appealed for calm.

"We are deeply concerned by the dangerous and deteriorating situation in Côte d'Ivoire, including recent reports of gross human rights abuses and potential massacres," Clinton said.

Meanwhile, in the mostly deserted streets of Abidjan, the crackle of gunfire and mortar explosions were constant noises, Oved said, adding "no one has done so much as stick their nose outside for the last few days."

Evacuation of UN workers

The UN began evacuating some 200 staff, following attacks on its headquarters from Gbagbo supporters.

A UN worker told The Associated Press that all "essential employees" were to leave on Sunday and were to be airlifted by helicopters from the base downtown to the airport, or to the northern city of Bouake.

Non-essential employees already left the country months ago.

The person was not authorized to speak to the reporters.

Rebels, UN trade blame

The UN and Ouattara's government have been trading accusations over the killings of hundreds of civilians in the western town of Duekoue. The international body accused Ouattara supporters of "extra-judicial executions" of more than 330 people in the town.

Ouattara's government Saturday night accused UN peacekeepers of abandoning civilians there to vengeful militiamen fighting for Gbagbo.

The Catholic charity Caritas said more than 1,000 were killed over three days last week in one Duekoue neighbourhood controlled by pro-Ouattara forces. Caritas said they did not know who did the killing.

With files from The Associated Press