Turkey will "hold the key" to what happens in Syria, US President-elect Donald Trump said on December 16.

Armed groups spearheaded by the jihadist HTS militia backed by Ankara brought down Syria’s Bashar al-Assad regime earlier this month.

By supporting the anti-Assad forces, "Turkey did an unfriendly takeover without a lot of lives being lost," Trump told a press conference at his residence in Palm Beach, Florida, as reported by Reuters.

On the same day Trump spoke, Turkey denied it was behind the HTS mobilisation in Syria, claiming it is a "false narrative".

Praising Nato member Turkey's "major military force" that "has not been worn out with war", Trump added: "Right now, Syria has a lot of, you know, there's a lot of indefinites ... I think Turkey is going to hold the key to Syria."

Turkey holds control over swathes of land in northern Syria. It took the territory during cross-border incursions against the Syrian Kurdish YPG militia, which it sees as a terrorist threat to Turkey given the Kurdish PKK insurgency Ankara has faced for 40 years.

The US has maintained around 900 troops in eastern Syria as a hedge against a resurgence of Islamic State. The US sees the YPG as an allied fighting force. YPG fighters east of the Euphrates river enjoy US air cover.

Trump was asked what he will do with the US troops in Syria after he takes office on January 20. His reply was vague. He changed topic, pointing to the strength of Turkey's military and emphasising his relationship with Turkish President Recep Tayyip Erdogan.

"Erdogan is somebody I got along with great ... He's built a very strong, powerful army," Trump said.

In what was an apparent reference to Turkey's Ottoman past, which included control over modern-day Syria, Trump added: "They've wanted it for thousands of years, and he got it, and those people that went in are controlled by Turkey, and that's OK."

Whether Trump will be sympathetic to voices in the US Congress on both sides of the aisle who argue that the YPG, as the indispensable fighting force that in an alliance with Washington eliminated the Islamic State caliphate that was formed in Syria and Iraq, should be protected from Turkish attacks, is a known unknown as things stand.

Also on December 16, there were reports that a US-brokered post-Assad ceasefire between Turkey and Syrian Kurdish fighters had collapsed.

In the days ahead of the offensive that caused him to flee to Moscow, Assad reportedly complained to ally Iran that Turkey was aiding militants who aimed to unseat him. Ankara has several times since the toppling of Assad recalled how earlier this year it offered him talks on resolving the 13-year-old Syrian conflict, but that he refused to attend such talks.