“We have been allowed to move everything from light weapons to heavy equipment mortars and missiles and our tanks,” Abu Issa, a commander of the militant group Levant Front, which runs the border crossing of Bab al-Salam, told Reuters on Thursday.
The militants, then, headed into the embattled border town of A’zaz in Syria’s northern Aleppo Province, he added.
The route across Turkey has become the only path for militants to enter Aleppo, after the Syrian army recently captured the main lifeline into the militant-held territory.
Another militant source said the Turkish army had stepped up delivery of arms and heavy military hardware in the last two days to reinforce militants facing a major offensive by Syrian forces.
Syrian troops have come within 25 miles (40 kilometers) of the Turkish border for the first time in over two years.
On Thursday, the so-called Syrian Observatory for Human Rights confirmed that hundreds of militants had crossed from the Turkish territory into A’zaz under the supervision of Turkish authorities in the last few days.
Ankara has been targeting YPG positions in northern Syria over the last few days in an attempt to stop Kurdish forces from reaching the Syrian border with Turkey, while Syrian forces have been making steady gains.
On Thursday, Prime Minister Ahmet Davutoglu announced that Turkish forces will continue to shell Kurdish positions on Syrian soil.
Turkey regards the YPG and its umbrella group the Kurdish Democratic Union Party (PYD) as an ally of the Kurdistan Workers’ Party (PKK), which has been fighting for an autonomous Kurdish region inside Turkey since the 1980s.
The YPG, which controls nearly Syria’s entire northern border with Turkey, has been fighting against the Takfiri Daesh terrorist group.
Turkey has been among the main supporters of the militant groups fighting to topple the Syrian government.