FILE - Turkish Foreign Minister Hakan Fidan attends a joint press conference with Russian Foreign Minister Sergey Lavrov in Moscow, Russia, on Aug. 31, 2023.AP
Strikes on Hasakeh province killed six workers at a brick factory and another worker in a separate factory, said Farhad Shami, spokesman for the Kurdish-led, US-backed Syrian Democratic Forces (SDF).
Earlier, a strike on the Kurdish-controlled region of Hasakeh hit a car, killing two people, said the Syrian Observatory for Human Rights, a Britain-based group with a network of sources on the ground.
Shami said Turkish drones had been targeting military positions, civilian infrastructure and a military vehicle since the morning.
He reported intensive overflights of areas controlled by the semi-autonomous Kurdish administration in northeastern Syria "following Turkish threats".
Turkey has also launched strikes on positions of the Kurdistan Workers' Party (PKK) in northern Iraq since Sunday, when two security officers were wounded in an attack in Ankara claimed by the PKK.
The US-backed SDF -- the Kurds' de facto army in the area -- led the battle that dislodged Islamic State group fighters from their last scraps of Syrian territory in 2019.
But Turkey views the Kurdish People's Protection Units (YPG) that dominate the SDF as an offshoot of the PKK.
'Declaration of war'
Turkish Foreign Minister Hakan Fidan alleged the perpetrators of the attack outside the interior ministry in Ankara had been trained in Syria and warned of reprisals against Kurdish fighters in northeastern Syria.
"It has become clear that the two terrorists came from Syria and were trained there," Fidan said in televised comments.
"From now on, all infrastructure, large facilities and energy facilities belonging to (armed Kurdish groups) in Iraq and Syria are legitimate targets for our security forces," he added.
"I recommend that third parties stay away from these facilities."
SDF commander Mazloum Abdi denied Wednesday that the two Ankara assailants had "passed through our region".
"Turkey is looking for pretexts to legitimise its ongoing attacks on our region and to launch a new military aggression," he said.
"The threat to target the region's infrastructure, economic resources and populated cities is a war crime, the thing we have witnessed before."
The Democratic Union Party (PYD), whose armed wing spearheaded the fight against IS in northern Syria with US backing, said on Thursday that "the Turkish foreign minister's statements are tantamount to a declaration of war".
The PYD called on the international anti-IS coalition to "take a stand" and be on its side.
Kurdish forces led the anti-IS offensive and are still supported by the United States.
They control a semi-autonomous Kurdish area in northeastern Syria which is regularly targeted by Turkish drone attacks.
Between 2016 and 2019, Turkey carried out three major operations in northern Syria against Kurdish forces.