ERBIL, Kurdistan Region — After being labelled a "terrorist organization" by the regime in Damascus, Kurdish anti-ISIS forces were shelled in Deir ez-Zor by forces loyal to Syrian President Bashar al-Assad, while in Afrin the Kurdish forces have also taken fire from Turkish positions.

The mostly-Kurdish People's Protection Units (YPG) comprise the backbone of the Syrian Democratic Forces (SDF), which has been the partnered ground force for the US-led international coalition against ISIS.

"Amid fierce battles against [ISIS] in the countryside of Deir ez-Zor, the regime and its militias tried to block the progress of the fighters by shelling," read an SDF Press statement regarding the events on Thursday.

The reported "heavy weapons" shelling occured on the east bank of the Euphrates in the Deir ez-Zor suburb of Al-Basira, according the SDF, was liberated a few days ago. The area is in east central Syria.

The Arab publication Asharq Al-Awsat reported Syrian Deputy Foreign Minister Faisal al-Miqdad labeled the SDF "a terrorist organization" during an interview on Iranian television.

"Tehran continues its pressure on the Syrian regime in Damascus to go into a military confrontation with the Washington-backed Syrian Democratic Forces," Kurdish sources told Asharq Al-Awsat.

Local Hawar News agency, linked to the YPG,  reported sand storms, and in "order to exploit this atmosphere, mercenaries launched an attack."

Hawar also reported that "the Baathist regime and Hezbollah had concluded an agreement with mercenaries on the Lebanese-Syrian border in September 22, following which mercenaries were transferred to Deir ez-Zor."

On Tuesday in northwestern Syria, Hawar reported "attacks by the Turkish occupation army" in several Kurdish cantons including Afrin and Shahba resulted in the deaths of three SDF fighters.

"These areas were targeted by dozens of mortars," reported Hawar. "The shelling resulting in financial damage inflicted to the civilians’ properties."

Although the US-led international coalition has been the SDF's primary backer, Russia has also supported YPG elements in Afrin.

To date the YPG and Assad regime have mostly avoided direct conflict, respecting the US-Russia de-conflication boundary that runs roughly along the length of the Euphrates in eastern Syria.

Iran, Turkey, and Russia began the eighth round of intra-Syrian talks, but there was no YPG or Kurdish delegation present due to reported objections from Turkey.

[Y]ou have to defeat the physical caliphate of ISIS; so long as you have a caliphate in the middle of Syria, it’s really hard to get a realistic, meaningful political process underway," US Special Presidential Envoy to the Coalition Brett McGurk said at a State Department on Thursday.