The United States opposes Turkey's possible military operation targeting the YPG/PKK terrorist group in Syria, Secretary of State Antony Blinken said Wednesday, citing instability concerns.

The top U.S. diplomat told a joint news conference with NATO Secretary-General Jens Stoltenberg that "any escalation there in northern Syria is something that we would oppose," underlining Washington’s support for "the maintenance of the current cease-fire lines."

Turkish President Recep Tayyip Erdoğan said Ankara is set to clear two areas of northern Syria near the Turkish border of terrorist elements in a bid to eliminate the terrorism threat from the region. The Turkish leader said the operation would target Tel Rifaat and Manbij towns to protect the nation and residents in northern Syria from the YPG/PKK terrorism threat.

"The concern that we have is that any new offensive would undermine regional stability (and) provide malign actors with opportunities to exploit instability," Blinken said.

The PKK is a designated terrorist group in the U.S. and Turkey. But the U.S. has partnered principally with the YPG, the PKK's Syrian affiliate, in northern Syria to counter the Daesh terrorist group in the region, a move that continues to roil bilateral ties.

"We continue effectively to take the fight through partners to ISIS within Syria and we don't want to see anything that jeopardizes the efforts that are made to continue to keep ISIS in the box that we put it in," Blinken said, using an alternate name for the Daesh terrorist group.

Turkey's warning for a possible operation comes amid the country's objections to Sweden and Finland's membership bids to NATO over their support for the YPG/PKK terrorist group and their inaction toward Ankara's security concerns.