The Turkey-backed rebels sent reinforcements to frontline areas in the countryside of Syria's Idlib Province over the past few days, a war monitor said Thursday.
The rebels' move coincided with arrival of the military backup of the Syrian army in the same region, according to the Syrian Observatory for Human Rights.
The situation in southern Idlib has been tense over the past few weeks with shelling and clashes between the rebels and the Syrian army.
The Observatory said the clashes continued on Thursday in areas in southern Idlib.
Four Syrian soldiers were wounded when the rebels fired a missile overnight on Syrian military positions, it added.
In parallel with the clashes, the Turkish forces sent 20 new military vehicles after mid-night to Turkish observation points in Idlib. The observation points were set up to monitor a cease-fire that was brokered by Turkey and Russia and went into force in March.