As mediators prepare to help negotiate an end to the conflict in Chad, France's President Nicolas Sarkozy said his country is prepared to use force to support the elected government of the oil-producing country.

"If France must do its duty, it will do so," he said Tuesday in response to a question on a possible French military operation in Chad. "Let no one doubt it."

There are about 1,800 French troops there already. While they have offered the government some support and helped French nationals and foreigners flee, French troops haven't yet been involved in combat. They did reportedly fire in self-defence in one incident.

On Monday, the United Nations Security Council authorized France and other countries to help Chad's government, under attack from rebels opposed to the rule of President Idriss Deby. They have said they will stop fighting only if Deby quits.

Chad is a former French colony. Deby first came to power through insurgency in 1990, and the elections he's won since haven't been seen as free or fair.

Rebels first showed up on the outskirts of N'Djamena, the country's capital, on Saturday.

There was heavy fighting on the weekend, but the rebels pulled back early Monday, saying they wanted to give civilians a chance to withdraw.

French military spokesman Capt. Christophe Prazuck said the rebels appear to be staying on the outskirts of N'Djamena.

"There has been sporadic shooting, but no combat," Prazuck said.

But heavy weapons had been used in earlier fighting, and he estimated that many have been killed.

An estimated 300,000 of N'djamena's 700,000 residents have fled into neighbouring Cameroon.

"As of this morning, frightened people were still crossing in a continuous flow," Ron Redmond, a spokesman for the UN refugee agency, told reporters in Geneva.

Paul Sitnam of World Vision told Canada AM on Tuesday that protecting refugees fleeing the fighting is one priority.

"And obviously just as important is making sure their basic needs are met -- that they have water, food, blankets and some shelter," he said from Dakar, Senegal.

The death toll from the fighting isn't known, but the Red Cross estimates more than 1,000 have been wounded.

Sitnam said much will depend on the success of diplomatic efforts.

Diplomats from the Republic of Congo and Libya are to arrive today as part of the African Union mediation mission.

France has agreed to protect the mediators.

Sudan, which shares a border with Chad, and the mediators will reportedly be talking with that nation.

Chad officials have accused Sudan's President Omar al-Bash of supporting the rebels.

"We are in direct war with Omar Bashir," Gen. Mahamat Ali Abdallah Nassour said Tuesday on Radio France Internationale. "It is Omar al-Bashir who wants to destabilize and Balkanize Chad."

The United States has called on Sudan to ask the rebels to call off their assault.

The violence is putting at risk a $300-million aid operation that helps 420,000 Darfur refugees and Chadians displaced by violence.

With files from The Associated Press