Turkish troops killed about 30 Syrian government soldiers in response to the deaths of six of Turkish military, Turkish President Recep Erdogan said on February 3.
"The operation is ongoing and ... according to preliminary results, 30 to 35 Syrians were killed," Erdogan told reporters at Istanbul airport before his flight to Ukraine.
The Syrian Observatory for Human Rights reported that 13 Syrian soldiers have been killed.
Erdogan also warned Russia, an ally of Syria, against intervening after Ankara retaliated against Syrian government forces.
"I want to tell the Russian authorities, in particular, that our opponent here is not you, but the [Syrian] regime, so you should not stand in our way," Erdogan said.
He added that representatives of the Turkish and Russian armed forces are in contact.
Earlier on February 3, Turkey's Ministry of National Defense reported that at least four Turkish soldiers were killed and nine wounded in "intense shelling" by the Assad forces in Syria's Idlib province. Subsequently, the number of deaths increased to six.
According to Erdogan, the shelling occurred even though the Turkish side had provided the coordinates of its forces, which were deployed to the province. According to the Turkish Defense Ministry, the Turkish soldiers responded to the fire.
The shelling came amid an offensive by the Syrian government army on the last rebel stronghold in the Syrian Idlib province and parts of Aleppo.
Turkish troops are deployed in some rebel-held regions to monitor the implementation of the previous ceasefire agreement.
Turkey, which has already taken in more than 3.5 million Syrian refugees, fears another wave of migrants if violence escalates in Idlib.
In mid-December, Syrian government forces, backed by Russian air power, resumed their offensive in Idlib province. It is the last territory west of the Euphrates River, which is controlled by the armed Syrian opposition. Hundreds of thousands of people in the province have fled their homes. Western countries fear that the offensive could trigger humanitarian crisis.