Bashar al-Assad threatened to attack a region held by U.S.-backed SDF, which has been dominated by PKK's Syrian branch, in northeastern Syria, saying in an interview broadcast on Russia Today channel on Thursday that American troops should leave the country.
The remarks reflect that despite pressure on multiple fronts, Assad is seeking to consolidate control after seven years of civil war.
With military backing from Russia and Iran, he has reclaimed most of the territory lost to rebels in the wake of the popular uprising that swept the country in 2011 and quickly descended into all-out civil war. But large patches of territory remain beyond his control, including the expansive region north of the Euphrates River that is administered by the PKK's Syrian branch YPG.
Speaking to the Russian channel, Assad said he has opened the door to negotiations with the YPG-dominated SDF while also preparing to "liberate by force."
Forces loyal to Assad and the SDF have clashed sporadically over the eastern oil province of Deir el-Zour. Last year, they led rival campaigns against the Daesh terror group, and maintain a protracted front against each other along the Euphrates.
The United States, which supports the YPG-dominated Syrian Democratic Forces, operates air bases and outposts in the Kurdish-administered region.
"The Americans should leave," Assad said. "Somehow, they are going to leave."
Assad is also under pressure from Israel over growing Iranian influence from Syria. Iran, in conjunction with the Lebanese militant group Hezbollah, now operates a network of militias recruiting from across the Mideast to fight on Assad's behalf and maintains a command structure separate from the Syrian government. Israel in recent months ramped up its strikes on alleged Hezbollah and Iranian positions and weapons depots inside Syria, sparking fears of a regional war.
In the TV interview, Assad maintained there are no Iranian troops in Syria, only Iranian officers advising the Syrian army. He denied reports that Iranians have been killed in Israeli strikes.
"Actually, we had tens of Syrian martyrs and wounded soldiers," he said.
The Britain-based Syrian Observatory for Human Rights, which monitors the war through a network of activists on the ground, says at least 68 Iranian and pro-Iranian forces have been killed in Israeli strikes since April.
Assad said Israeli strikes destroyed a "big part" of Syrian air defenses, but added they have been rebuilt, "stronger than before, thanks to Russian support."
The U.S. and Russia, while backing rival sides in Syria's war, have coordinated their maneuvers in Syria and largely avoided direct confrontation.
But in February, U.S.-led coalition airstrikes killed several Russian private contractors that appeared to be advancing with pro-government forces on a position held by YPG-dominated SDF forces in Deir el-Zour. Russia has maintained the Russian contractors in Syria are in the Mideast country of their own volition and are not the responsibility of the Kremlin.
In the interview, Assad said U.S. and Russian forces would have come in direct conflict long ago in Syria if it were not for Russia's prudence and judgment.