Large convoys of Turkish military vehicles have driven to the province of Idlib, a total of 1,000 vehicles, reports the Reuters news agency.
The troop movements are seen as a response to Syrian government forces, backed by Russia, attacking Idlib in intense raids.
Hundreds of people have been killed in the offensive and 586,000 have moved in the direction of the Turkish border according to the UN.
Most refugees end up in temporary camps on the border with Turkey, which is closed to the refugees.