A Syrian Kurdish official says negotiations are ongoing between the government in Damascus and Kurdish officials on how to fill the gap following the withdrawal of U.S. troops from the country.

The official, who spoke Saturday on condition of anonymity because of the talks' secrecy, said Syrian Kurdish officials have visited Russia which is sponsoring the talks between the government and the Kurd-led militia that control nearly a third of the country.

The official said negotiations are ongoing and "the atmosphere is positive."

President Donald Trump announced in mid-December that the U.S. will withdraw all of its 2,000 forces in Syria.

The main U.S.-backed Kurdish-led Syrian Democratic Forces has expressed concerns over the planned withdrawal as Turkey has threatened to launch a military operation against Kurdish fighters in Syria.