World Bulletin / News Desk

The U.S. will continue to trust the YPG to fight ISIL on the ground in northern Syria, unless proven otherwise, the State Department said Friday.

The YPG is the armed wing of PYD -- the Syrian branch of the terrorist PKK group.

Though Turkey considers all three outfits terrorist, the U.S. designates only the PKK as such.

Toner's comments came two days after a deadly blast in the Turkish capital of Ankara killed 28 people and wounded 81 others.

Turkey quickly determined that the alleged attacker was a member of the YPG, but the U.S. has been reluctant to confirm those findings.

The American ambassador in Ankara, John Bass, on Thursday went to the Turkish Foreign Ministry "where he received preliminary results of the investigation”, according to State Department spokesman Mark Toner, who declined to provide additional details.

The dynamics of the links between Turkey, the U.S. and Syrian Kurds has placed a strain on the relationship between Ankara and Washington.

The Obama administration has lauded Ankara's efforts in the fight against ISIL, however, and White House spokesman Josh Earnest said Friday that Turkey's contribution has been "substantial."

"There is important progress that we made over the last year in strengthening and solidifying the relationship between the United States and Turkey, and that has yielded important benefits for both our countries, particularly in enhancing our effort to degrade and ultimately destroy ISIL," he said.

But Turkey has recently pressed the U.S. on its support for the YPG and has even suggested the Americans choose between its NATO ally and a group Ankara considers a terrorist outfit.

Turkish President Recep Tayyip Erdogan's suggested that the YPG is using American weapons while operating in northern Syria, a claim substantiated by media reports of the group using American tanks and of it hitting moderate Syrian opposition forces in northern Syria.

Toner said the U.S. did not provide any weapons to the group.

He also brushed aside reports of attempts by the YPG to establish a semi-autonomous area in northern Syria, saying the U.S. is aware of the reports but it has been candid with the YPG about the need for "good governance" and allowing refugees to return to areas once they are retaken from ISIL.

But the American spokesman said the U.S. wanted Turkey to halt its shelling of YPG positions along the Turkish border with Syria because it continues "to escalate" the problem.

YPG is currently taking additional territory outside of Afrin, including areas close to the town of Azaz and the Manakh Air Base in northern Syria, which are areas close to the Turkish border.

Turkey has since been shelled PYD and PKK positions in the northern Syria for four consecutive days in retaliation to artillery fire from PYD forces based around Azaz, located in Aleppo’s northern countryside just 6 kilometers (4 miles) from the Turkish border.

The exchange of fire came after the YPG's recent advance into Azaz -- the scene of recent heavy fighting.

Meanwhile, a task force recently created d to oversee a “cessation of hostilities” agreement in Syria, will meet later Friday in Geneva to discuss the deal, according to Toner.