The attack in Deir el-Zour province in northeastern Syria occurred in crowded battle space. USA -backed Kurdish-led forces have been fighting for control of Deir el-Zour with rival Russian-backed Syrian troops that are reinforced by Iranian-supported militias. USA forces have pivoted their focus from the fight against ISIS to fighting Russian-backed Syrian forces. Previous friction was reported before, but Wednesday's incident appeared to be the largest since a year ago.
Relations have also been strained by Washington's failure to extradite a US -based Muslim cleric blamed by Turkey for a failed coup attempt against Erdogan in 2016.
The SDF and the coalition targeted the attacking forces with air strikes and shelling after "20 to 30 artillery and tank rounds landed within 500 metres (yards) of the SDF headquarters location", a United States official said. More than a hundred pro-regime fighters were killed.
"The no-holds-barred nature of this assault is evidenced by reports that at least nine medical facilities, six of them in Idlib and three in Eastern Ghouta, were hit by airstrikes".
"What would we talk about with a murderer who has killed a million of his citizens", Erdogan said in his address to mukhtars- heads of Turkish villages and neighbourhoods-at the presidential complex in Turkey's capital, Ankara, as quoted by TRT World.
In Kuwait, he will attend a meeting of the "Global Coalition to Defeat ISIS", the first gathering at this level since US-backed local forces drove the jihadist group out of its Syrian bastion Raqa, a statement said. It alleged the incident showed that Washington was not interested in fighting Islamic militants but wanted "to seize and hold Syrian economic assets".
The United States backed the plea but Russian Federation - a longtime ally of Syria's government - shrugged it off.
But the USA denies those connections and sees the YPG as a key ally in the battle against the Islamic State.
Turkish police detained leading members of several Kurdish and leftist parties on Friday, the co-leader of the main pro-Kurdish HDP party said, describing it as an attempt to hamper preparations for the annual HDP congress on Sunday.
Syrian government airstrikes killed about 76 civilians, including 20 children, and injured 140 others on Thursday, the fourth day of attacks against a rebel-held region, a war monitor reported.More news: US Misses Opportunity for Korean Peace at Olympics
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He added: "Even by Syria's atrocious standards, these are exceptionally deplorable developments - and a cruel irony given that both have been declared "de-escalation areas".
The clashes prompted the coalition response with land-to-land missiles and airstrikes, the Observatory said.
"Over 300 primary, secondary and high schools have been closed down", she added.
The U.S. airstrike coincides with escalating violence in Syria.
The YPG - trained, armed and supported by the U.S. to fight against the Islamic State of Iraq and the Levant (ISIL) - control a swath of land in northern Syria. Siraj Mahmoud of the Syrian Civil Defense, also known as White Helmets, said 58 people were killed. "Eastern Ghouta is experiencing a Middle Ages-style siege".
"Excuse me but no state would ignore a terror organisation growing like a tumour next to it", he said.
State Department spokesperson Heather Nauert called out Russian Federation on Thursday for enabling the Syrian regime's use of chemical weapons on civilians. The United Nations called on Tuesday for a humanitarian truce of at least one month to allow for aid deliveries and evacuations of the wounded.
The Kremlin said Putin and Macron discussed the Syrian peace process in the phone call. It is also unclear where the incident took place.