France is deploying 200 soldiers to help secure Chad's eastern border with Sudan's conflict-torn Darfur region.
Darfur has been described as the world's worst humanitarian crisis
The French Ambassador to Chad, Jean Pierre Bercot, said the troops would also bring humanitarian aid to tens of thousands of Darfur refugees in Chad.
Sudan-backed Arab militias have driven about a million civilians from their homes and mounted raids inside Chad.
Sudan said that despite reservations it would comply with a UN resolution ordering it to rein in the militias.
Sudanese Foreign Minister Dr Mustapha Osman Ismail said government's Council of Ministers' would take a final decision at a meeting on Sunday.
Up to 50,000 people have died since the conflict began in early 2003.
The Janjaweed, the main Arab militia group allied with the government, has been blamed for mass rapes, killings and burning of villages in Darfur.
France has about 1,000 troops in Chad, who until now have been helping to promote stability and train Chadian forces for peacekeeping duties.
Ambassador Bercot told the BBC from Chad's capital, N'Djamena, that 200 French soldiers would now be deployed to Chad's eastern frontier with Sudan to help the aid effort and watch out for possible incursions.
"The French government and President Chirac wanted our troops here in Chad to assist the African Union in its observation role, as well as in securing the area on the Chadian side of the border," he said.
Mr Bercot said that for the time being the French contingent was to remain inside Chad after he was asked if the troops would engage with the Janjaweed if the militias crossed the border.
He stressed that the French troops would work alongside Chadian forces "with the complete authority and co-operation" of the government in N'Djamena.
Given that the frontier stretches through 1,200 kilometres (745 miles) of inhospitable terrain, this could be no more than a token presence, the BBC's Africa editor, Grant Ferrett, reports.
Nevertheless, the French military presence adds to the impression that the rest of the world is becoming more willing to take action over Darfur, our editor adds.
Aid agencies in Chad who have been struggling to help some 180,000 Sudanese refugees have welcomed the French move to use its military might to help supply the refugee camps.
A French military cargo plane with humanitarian aid had already left for eastern Chad.
The US-drafted resolution demands that Sudan to make good on promises it made on 3 July to rein in the fighters.
It calls for UN Secretary General Kofi Annan to issue a report in 30 days on the progress made in each of those areas.
The resolution was only adopted after the US dropped the word "sanctions" and added economic and diplomatic "measures".
Sudan's UN ambassador Elfatih Erwa, and its ambassador to the African Union, Osman al-Said, separately said Khartoum would comply.
"We are not happy with the resolution, but we are going to implement it - we have no other option," Mr al-Said told reporters in the Ethiopian capital Addis Ababa earlier this week.
US Secretary of State Colin Powell said during a visit to the Middle East: "They [The Sudan government] can say whatever they wish to say. The Security Council has spoken (and) in a rather strong vote."