U.S. Republican Senator Lindsay Graham shifted his stance once again on Turkey's fight against terror groups in the area east of the Euphrates River in northern Syria, launching a campaign to force Ankara to halt Operation Peace Spring.

Graham on Monday threatened Turkey with sanctions if Ankara would not immediately halt its anti-terror operation against People's Protection Units (YPG) terrorists in Syria.

"Will lead effort in Congress to make Erdogan pay a heavy price," Graham tweeted, referring to Turkey's President Recep Tayyip Erdoğan.

But just a few months before Graham changed his tune, the senator had admitted that there was evidence of a "strong link" between the YPG and the PKK, a terrorist organization recognized by both the U.S. and EU.

Graham held a news conference in February in Ankara and told reporters that there was sufficient evidence to prove that both organizations had links, adding that former U.S. President Barack Obama "created a nightmare" for Turkey by arming elements of the YPG that are "clearly tied to the PKK."

He referred to the YPG as the "political wing" of the PKK, noting that he had been aware of the fact that the Obama administration's Syria policy was wrong.

"I knew what arming the YPG/PYD meant for Turkey when I learned about it," Graham said.

"Here is the promise I made to President Erdoğan: I'll try my best to fix the problem we've created for your country," he added.