Forces entered the country's Afrin province today just 24 hours after pounding the region with airstrikes.
Turkish Prime Minister Binali Yildirim reportedly said they are targeting US-backed Kurdish fighters.
Shocking pictures show dozens of tanks and armoured vehicles crossing over the border in a terrifying display of military might.
But the Syrian-Kurdish YPG militia has denied there is a full-scale invasion underway, claiming forces clashed in Afrin but Turkish soldiers were beaten back.
YPG official, Nouri Mahmoudi, said "all the Turkish military's ground attacks against Afrin have been repelled so far and they have been forced to retreat."
A statement from the militia said: "Our people are holding on to their land and do not accept surrender... we repeat our determination to protect our people in Afrin against the attacks."
Turkey has claimed the massive movement of military hardware into the country is simply to create a 30km-deep "safe zone" in the north of the country.