Syrian President Bashar al-Assad has called U.S.-backed Kurdish fighters "traitors," according to an online statement from his office on December 18.

Both Assad's government, which is backed by Russia, and the Kurds, backed by a U.S.-led coalition, have fought the extremist group Islamic State (IS) in Syria in recent months.

"When we talk about those referred to as 'the Kurds,' they are in fact not just Kurds. All those who work for a foreign country, mainly those under American command...are traitors," the statement quoted Assad as saying.

He spoke during a meeting with Russian Deputy Prime Minister Dmitry Rogozin at Hmeimim air base, the center of Russia's military campaign in support of government forces.

Kurds account for an estimated 15 percent of Syria's population, and their forces currently control a large part of the country.

Assad said he also welcomed a United Nations role in Syrian elections as long as the country's sovereignty was protected -- suggesting he would resist any attempt to remove him from power as part of a future political transition.

After the meeting, Rogozin said that Moscow would be the only country to take part in rebuilding Syrian energy facilities.

Russia has given Assad crucial military and diplomatic backing throughout Syria's nearly seven-year war, which began with a government crackdown on pro-democracy protesters.

The war has also badly damaged Syria's economy and infrastructure.

"President Assad said today that Syria has no desire to work with companies from countries which betrayed Syria at a certain moment," Rogozin said.

Rogozin was speaking a week after President Vladimir Putin ordered "a significant part" of Moscow's military contingent in Syria start withdrawing, declaring their work largely completed.

With reporting by RIA, Rossia-24, Reuters, and AFP