US Defence Secretary Jim Mattis said French special operations forces arrived in Syria over the past two weeks to help boost US-led efforts against the Islamic State group.

Speaking to senior lawmakers in Washington, Mattis responded to a question about whether the United States was planning on pulling out of Syria - something President Donald Trump has said would happen "very soon."

Right now, "we are not withdrawing," Mattis told the Senate Armed Services Committee.

"You'll see a re-energised effort," he said.

"You'll see increased operations on the Iraqi side of the border, and the French just reinforced us in Syria with special forces here in the last two weeks. This is an ongoing fight right now."

On Tuesday, Trump appeared to walk back his vow to yank US troops from Syria, saying the United States wanted to "leave a strong and lasting footprint​" in the country.



Currently, about 2,000 US troops are in Syria, most of which are commandos.

Even after IS - which still controls two pockets of territory along the middle Euphrates River Valley - are defeated, the US military wants to maintain a presence in Syria to prevent the extremist group from returning.

Mattis said he wanted to see more "regional support" for the anti-IS fight and told lawmakers he was "confident that we would probably regret it" if the US does not contribute to a long-term holding force in Syria.

France is a longstanding member of the international coalition fighting IS in Iraq and Syria, and helped bombard the extremists in the Mosul area during the Iraqi operation to recapture the city.

France, along with the US and Britain, also took part in the April 14 cruise missile strikes against Syrian President Bashar al-Assad's chemical weapons-related facilities in the wake of an alleged chlorine attack on the city of Douma.