Turkey and the US-backed YPG forces — which have been helping the coalition fight ISIS in Syria — have been clashing off and on since at least April.
At the end of that month, the two sides exchanged rocket fire, which Turkey says killed 11 YPG fighters. In early July, Turkey deployed troops to the Kurdish-held border in northwest Syria, which the YPG commander called "a declaration of war."
YPG and Turkish-backed rebels — who the YPG call mercenaries — clashed in northwest Syria on July 17, Reuters reported. The YPG said it killed three Turkish-backed rebels and wounded four more.
Turkey views the YPG as a terrorist group and extension of the PKK, which has been trying to set up its own Kurdish state within Turkey for decades. And the US has placed itself right between the two sides.
President Trump (left) and President Erdogan of Turkey (right). (Photo from Moscow Kremlin.)
Turkey is the third-largest purchaser of US weapons, and in early May, the US began supplying weapons to the YPG to help in the coalition's fight against ISIS.
The latter move has angered Turkey even more than the US's unwillingness to extradite Fethullah Gulen, according to Kemal Kirisci, a senior fellow at the Brookings Institution. Gulen is a Muslim cleric who lives in Pennsylvania and has been accused by Turkey of organizing the attempted coup in 2016.
These developments have coincided with Turkey's gradual drift toward Russia. Ankara and Moscow recently agreed to build a pipeline through Turkey, which allows Moscow to bypass Ukraine, and last week, Turkey signed an agreement with Russia for the $2.5 billion purchase of Moscow's advanced S-400 missile-defense system.
SA-400. (Photo by Vitality Kuzmin)
Turkey is also one of the three guarantors, along with Russia and Iran, of the Syrian de-escalation zones.
Kirisci told Business Insider that he can't prove there is a direct connection between Turkey moving closer to Russia and the US supplying the YPG with weapons, but he did say, "You don't need to be escorted to a village that you can see in the distance."
"[Turkey] has been pissed off at the US for a long time," Aaron Stein, a senior fellow with the Atlantic Council, told Business Insider. "They're not leaving NATO, but they're trying to show everyone that they have options."
Photo from Wikimedia Commons.
Stein added that "the US is partly to blame" for increased tensions between Turkey and YPG, but, he said, "all sides have blood on their hands in this thing."
Kirisci also said that "the Pentagon is running its own show," and the US State Department doesn't appear to be checking its decisions.
"We are concerned [about increased tensions between Turkey and YPG] but doing everything we can to defuse the situation," Marine Corps Maj. Adrian J.T. Rankine-Galloway, a Pentagon spokesman, told Business Insider.
Rankine-Galloway said that the weapons, which are tracked with serial numbers, will be collected from the YPG after the fight with ISIS concludes.
A fighter for the Free Syrian Army loads a US-made M2. The YSA is supplied by the US, but opposes the YPG, also supplied by the US. Photo from Wikimedia Commons.
But Kirisci and Stein both said they were doubtful that the US will be able to collect the weapons from the YPG. "They'll try, but it won't happen," Stein said.
It's "to be determined" if a full-scale war will break out between Turkey and the YPG once the fight against ISIS is over, Stein said. The US probably won't leave northwest Syria for a while, and its presence will help deter fighting between the two sides.
The skirmishes that have happened between Turkey and the YPG have happened in areas where there is no US troop presence.