Turkish-backed forces have started a "serious operation" in Syria's Idlib, President Recep Tayyip Erdogan said on Saturday, but troops had not yet entered the northern province. "Now this step has been taken, and it is underway".
The US mission to Turkey said on Sunday it was reducing visa services after one of its employees was detained last week, saying it needed to "reassess" Turkey's commitment to the security of its personnel.
More than 330,000 people have been killed in Syria since the conflict began with anti-government protests in March 2011.
In another front, Syria's army and its allies have encircled Islamic State in the city of al-Mayadin, southeast of Deir al-Zor, in eastern Syria, a Syrian military source said yesterday. Turkey has threatened to clear the province of Kurdish forces that it regards as belonging to a terrorist group with links to the PKK, which has long battled for autonomy in Turkey's southeast.
Late on Saturday, Turkey deployed tanks and military vehicles on its Syrian border, building up military presence, the report added.
The move comes as Turkey, along with Russian Federation and Iran, prepare to set up de-escalation zone in Idlib in line with accords in peace talks in Astana aimed at ending the Syrian war.
The province is dominated by jihadist groups and Mr Erdogan has said he will not allow a "terror corridor" on the Turkish border.
The FSA groups supported by Turkey are now ready to enter Idlib, Mustafa Sejari, a senior official in the Liwa al-Mutasem group said.
The Turkish army is amassing tanks and commandos ahead of a joint mission with Russian Federation and Iran to monitor a ceasefire agreement and pacify a rebel stronghold in northwest Syria.
Along with Iraq's central government, Turkey, the US, Iran, and the United Nations have spoken out against Monday's illegitimate poll, warning it would distract from the ongoing fight against ISIS and further destabilize the region.
He pointed out that bringing peace to Syria requires both military and political actions, and now there are three countries, namely Russia, Turkey and Iran, that can resolve the Syrian crisis.
The intermittent clashes were reported near the town of Kafr-Lusin on the border in the northern countryside of Idlib province in northwestern Syria, Xinhua cited local media as reporting. Turkey, however, has backed rebels seeking Assad's ouster.