Syrian President Bashar al-Assad warned US-backed Kurdish forces he wouldn't hesitate to use force to retake one-third of the country they currently control.
Assad also warned in an interview with Russia Today on Thursday that the United States should learn the lesson of Iraq and remove its troops from Syria.
"The only problem left in Syria is the SDF," Assad said, referring to the Kurdish-led Syrian Democratic Forces, which spearheaded battles against the Islamic State of Iraq and the Levant (ISIL, also known as ISIS).
"We're going to deal with it by two options: the first one we started now opening doors for negotiations, because the majority of them [SDF] are Syrians. Supposedly they like their country, they don't like to be puppets to any foreigners," Assad said.
"If not, we're going to resort ... to liberating those areas by force. It's our land, it's our right, and it's our duty to liberate it, and the Americans should leave. Somehow they're going to leave," he added.
"They came to Iraq with no legal basis and look what happened to them. They have to learn the lesson. Iraq is no exception and Syria is no exception. People will not accept foreigners in this region any more."
Russia-US confrontation
Both the SDF and Russian-backed Syrian government troops are engaged in separate operations against ISIL in eastern Syria, creating a highly volatile situation.
Assad said a confrontation between Russia and US forces over Syria had been narrowly avoided.
"We were close to having direct conflict between the Russian forces and the American forces," he said. "Fortunately it has been avoided - not by the wisdom of the American leadership, but by the wisdom of the Russian leadership."
'Animal Assad'
Responding to US President Donald Trump's description of him as "Animal Assad", the Syrian leader shot back: "What you say is what you are." Trump called Assad "an animal" after a suspected poison gas attack on a rebel-held town near Damascus in April.
A US-led wave of Western missile strikes on Syrian government targets across the country last month raised fears of a Russian response and full-blown internationalisation of the seven-year-old conflict, which has killed hundreds of thousands and drove millions out of the country.
Air strikes by US ally Israel against Iranian-backed forces have raised fears the devastating war could escalate further.
Israel, which is deeply alarmed by Tehran's influence in Syria, earlier this month said it destroyed dozens of Iranian military sites in Syria, after Iranian forces fired rockets at Israeli-held territory for the first time.
