At least 36 pro-Syrian government troops have been killed by a Turkish air strike in the region of Afrin, a monitoring group says.
The strike targeted a camp at Kafr Jina in the northern Syrian region, the Syrian Observatory for Human Rights (SOHR) said.
The pro-government troops entered Afrin two weeks ago to back Kurdish forces.
They are fighting a Turkish military offensive that was launched to clear Kurdish groups from Afrin.
Turkey considers the Kurdish militiamen there terrorists.
The Syrian government has denounced the offensive as a "blatant attack" on its sovereignty and, according to state media, forces were sent in to support the Kurds.
The air strike followed one of the bloodiest days for Turkish troops since they began the offensive in January.
Eight Turkish soldiers were killed and another 13 were injured on Thursday in fighting in Afrin.
Five "heroic comrades fell as martyrs and seven were wounded", an initial statement from Turkey's military said. A second statement announced three more soldiers had been killed and six more wounded.
No official details of the clashes were given but the private Dogan news agency said Kurdish fighters used tunnels to ambush Turkish special forces in the Keltepe district.
A Turkish helicopter sent in to rescue the wounded was hit and had to turn back, the report added.
Thousands of civilians in Afrin have fled their homes since Turkey's offensive began.
The Turkish government says the Kurdish People's Protection Units (YPG) militia is an extension of the banned Kurdistan Workers' Party (PKK), which has fought for Kurdish autonomy in south-eastern Turkey for three decades.
The YPG denies any direct organisational links to the PKK.
Neither side has released much information about fatalities, making the death toll in Afrin difficult to gauge.
The UK-based SOHR says more than 141 civilians have died but Turkey denies this, saying only combatants are targeted.
Yet another new flashpoint?
Analysis by Sebastian Usher, BBC Arab Affairs Editor
When pro-government militia forces edged into Afrin last month, it wasn't clear what their strategic purpose would be.
Videos showed a small group of militiamen being welcomed to Afrin city by Kurds there as their saviours. But it didn't seem likely that they would play much more than a symbolic role, allowing the Syrian government to vaunt a new territorial initiative but at no major risk.
In fact, it seemed that it might be a way of de-escalating the latest conflict in Syria after Turkey launched its operation against Kurdish fighters there.
A deal to allow the Syrian government to take over much of the control of the area might suit many of the parties involved. It might even be a less bad option for Turkey, allowing it to turn down the intensity of its offensive.
But if the reports are true that pro-government forces have been badly hit by Turkish airstrikes, that would appear to undercut this interpretation, raising the prospect of yet another new flashpoint in Syria.