Turkey's official news agency has said that Turkey-backed Syrian opposition forces have reached a strategic highway in northeastern Syria as Turkey's offensive against Syrian Kurdish fighters enters its fourth day.
Anadolu news agency said on Saturday the forces have arrived at the M-4 highway that connects the Syrian towns of Manbij and Qamishli. The road is about 30 kilometres south of the Turkish border.
Turkey has said it aims to push back Syrian Kurdish People's Protection Units, or YPG, which it considers terrorists for its links to a decades-long Kurdish insurgency within its own borders.
Mr Erdogan said on Friday Turkey won't stop until the YPG, who forms the backbone of the US-backed ground force against the Islamic State, withdraws below a 32 kilometre deep line.
Turkish forces stepped up their bombardment around a town in north-east Syria on Saturday, the fourth day of the offensive, after US troops in the region came under artillery fire from Turkish positions.
The United States has ramped up its efforts to persuade Ankara to halt the incursion against the US-backed Kurdish forces, saying Ankara was causing "great harm" to ties and could face sanctions.
Turkey opened its offensive after US President Donald Trump spoke by phone on Sunday with Mr Erdogan and withdrew US troops who had been fighting alongside Kurdish forces.
On Friday evening, Mr Erdogan dismissed mounting international criticism of the operation and said Turkey "will not stop it, no matter what anyone says".
The death toll among Syrian Kurdish-led fighters battling a Turkish offensive has risen to 74, most of whom have been killed in the Tel Abyad area, the Syrian Observatory for Human Rights said on Saturday.
Observatory Director Rami Abdulrahman also said 49 fighters with Turkish backed Syrian rebel groups had been killed since the assault began on Wednesday.
The death toll among civilians in Syria had climbed to 20 after two people died in the city of Qamishli, he said. Most of the civilian deaths were also in Tel Abyad, a border town that is one of the focal points of the operation.