The French news agency, AFP, reports the commandos are not participating in combat in the so-called Manbij pocket and are restricted to advisory and training roles. U.S. officials have also insisted about 300 American special forces in northern Syria and embedded with the Syrian Democratic Forces are not involved in combat.

"The offensive at Manbij is clearly being backed by a certain number of states including France. It's the usual support - it's advisory," a French defense ministry official told AFP. Until now France has only acknowledged a ground deployment of around 150 members of its special forces in Iraq's Kurdish region.

French defense minister Jean-Yves Le Drian told a French television channel Friday that France was supplying arms and providing aerial support as well as offering tactical advice, but didn't mention a special forces deployment.

Airstrikes intensifying

The confirmation of French ground assistance to the Kurdish-led Syrian Democratic Forces, the SDF, came as Syrian government warplanes intensified airstrikes on rebel-held districts of Aleppo. Airstrikes Wednesday killed at least 20 people and damaged three hospitals in the rebel parts of the city, according to local political activists and rescue workers known as the White Helmets.

Mainstream rebels in the Free Syrian Army who oppose the government of leader Bashar al-Assad, but shun the SDF, have expressed anger at backing the mainly Kurdish forces have received from the United States, complaining they are not receiving the same kind of close-air support or arms resupplies they need to fend off an unfolding Russian-backed Assad regime offensive.

Offensive at Manbij

The SDF, a U.S.-backed alliance dominated by the Kurdish People's Protection Units, or YPG, but also including a mix of small Sunni-Arab armed groups and some Syriac and Turkmen community defense forces, has made significant progress in its offensive on Manbij, an important waypoint between the Turkish border and the militants' de facto capital in Syria, Raqqa.

The SDF claimed Thursday to have almost surrounded Manbij after capturing Amyal hill, 12 kilometers to the southwest of the IS stronghold. In the south, SDF forces are just three kilometers from the town's limits, and to the northwest, there was heavy fighting Thursday focused on the village of Akhdar, where IS still controls a road into Manbij.

"We have reached the road that links Manbij and Aleppo, from the west," said Sharfan Darwish, an SDF spokesman. The SDF said its fighters were close enough to Manbij to be able to fire on IS militants.

Some SDF officers claimed the town would soon fall, and cited the apparent evacuation from Manbij of some IS fighters, which they say started earlier this week with convoys including dozens of vehicles.

"A large number of IS terrorists have already escaped the city, using the western exit. This means that the collapse of the group in Manbij is very near," SDF officer Habun Osman told the local ARA News.

But SDF spokesmen said movement into the town would be cautious, mainly because of IS mines and booby-trap explosives. Some observers also expected a last ditch defense of Manbij by a rearguard IS force.

Further west, anti-Assad rebels with the FSA and Islamist factions appeared also to be having success, pushing back an IS offensive on the town of Marea. The rebels' desperate defense of the town close to the Turkish border was helped by Turkish artillery shelling and U.S.-led coalition airstrikes of IS positions.

FSA and local activists said IS fighters started to withdraw from around Marea in the face of the airstrikes and shelling, lifting a siege they imposed on the town nearly a month ago. "It seems they (IS) can't keep several fronts open at the same time," said Rami Abdulrahman, director of the pro-rebel monitoring group the Syrian Observatory for Human Rights.

The loss of Manbij would be a serious blow to IS, say U.S. officials, and would amount to the biggest reversal the terror groups has sustained in Syria since Assad regime forces captured the town of Palmyra in March.

U.S. Central Command said U.S. warplanes had conducted more than 105 strikes in support of the SDF offensive to seize Manbij.