“We want to see all countries use their influence – use their leverage – to push for de-escalation, protection of civilians and ultimately, a political process forward,” state department spokesman Matthew Miller told reporters.

Asked if the US was sending the message to Turkey to protect the Kurdish population, Miller said: “We’re going to continue to make clear to every party and every country who engages with parties inside Syria that they do everything possible to protect civilians.”

Hayat Tahrir al-Sham (HTS), an Islamist group with backing from Turkey, and allied factions staged a lightning offensive last week from northwestern Syria near the Turkish border, wresting swathes of territory from government control, including Syria’s second city Aleppo.

Days later, Turkish-backed groups launched an attack on the strategic Kurdish-held Tal Rifaat area.

The US during the height of the war said that Assad, who is backed by Iran and Russia, had lost legitimacy but it later said it was not a priority to remove him, seeing no better alternative in the rebels.

“Nothing has changed with respect to our policy. Assad is a brutal dictator with blood on his hands,” Miller said.

“The organisation that launched this offensive over the weekend is a terrorist organisation designated as such by the US. We certainly do not support that organisation in any way, shape or form.”

Washington maintains around 900 US troops in Syria for the stated goal of fighting the Islamic State group and has forged an alliance with the Kurdish-led Syrian Democratic Forces (SDF).

However, Turkey associates the SDF with Kurdish militants fighting within its own borders.

President-elect Donald Trump in his last term in office ordered the withdrawal of US troops after appeals from Turkish president Recep Tayyip Erdogan but backtracked after talks with French president Emmanuel Macron.