A Turkish air strike on Monday killed 20 Kurdish security personnel and wounded dozens at a training center for police in Kurdish-held northeast Syria, a war monitor said.
The Syrian Observatory for Human Rights, a UK-based monitor, said that 20 people had been killed and around 50 wounded after a Turkish war plane targeted a training centre belonging to Kurdish internal security forces, known as the Asayish, on the outskirts of Al-Malikiyah.
The Kurdish force reported the strike in a statement, saying that "a number of our forces were killed and others wounded."
AFP correspondents said authorities in the area have called for blood donations.
Amid the chaos of Syria's long-running civil conflict, Syria's Kurds have carved out a semi-autonomous area in the country's northeast.
Since Thursday, Turkey has been bombing sites in the area, hitting civilian and military targets and infrastructure and causing casualties, according to Kurdish authorities.
Turkey's Defense Ministry said Friday it had launched the new wave of airstrikes in retaliation for an attack in Ankara earlier this month that wounded two security personnel.
A branch of the Kurdistan Workers' Party (PKK) — listed as a terror group by Ankara and its Western allies — claimed responsibility for the first bombing to hit the Turkish capital since 2016.
Turkey launched strikes on PKK positions in northern Iraq hours after the October 1 attack, with Foreign Minister Hakan Fidan saying days later that the assailants "came from Syria and were trained there."
The US-backed, Kurdish-led Syrian Democratic Forces led the battle that dislodged Islamic State group fighters from their last scraps of territory in Syria in 2019.
Turkey views the Kurdish People's Protection Units (YPG) that dominate the SDF as an offshoot of the PKK.
The SDF, the Kurds' de facto army in the area, denied the Ankara assailants had passed through the area.
Turkish bombings had mostly subsided over the weekend after strikes hit energy infrastructure, including power stations and oil facilities, on Thursday and Friday, killing at least 15 security personnel and civilians, according to the Kurdish authorities.
Since 2016, Turkey has carried out successive ground operations to expel Kurdish forces from border areas of northern Syria, and Turkish President Recep Tayyip Erdogan has made threats of a new incursion.
Turkey supported early rebel efforts to topple Syrian President Bashar al-Assad and maintains a military presence in northern stretches of the war-torn country that angers Damascus.
In November last year, Turkey launched air strikes on Kurdish-held areas of Syria and Iraq in response to a bombing in Istanbul that killed six people.
The conflict in Syria has killed more than half a million people since it began in 2011 with a brutal crackdown on anti-government protests, spiraling into a devastating war involving foreign armies, militias and jihadists.