It took place on the Syrian side of the Atmeh crossing, west of Aleppo. A photo sent by a witness in the area, purportedly of its aftermath, showed the bloodied corpses lying on the ground.
Daesh claimed the attack in an online statement, Reuters reported.
The witness said most of the militants were from the Failaq al-Sham group, which has been fighting alongside other Turkish-backed factions in Ankara's offensive, dubbed "Euphrates Shield".
That operation, taking place along the border northeast of Aleppo, has also targeted Kurdish rebels.
The militants use the Atmeh crossing to move between Idlib province, through Turkey.
Residents told Reuters they also use it to evacuate wounded fighters.
Among the dead from the Atmeh blast were the head of the top civil judicial body in militant-held eastern Aleppo, Sheikh Khaled al-Sayyed, and a judge who worked with him, a witness and a militant official said.
Aleppo, further to the east, has been divided for years between government- and militant-held areas. The opposition have set up their own administrative bodies in the east.
Government forces have encircled eastern Aleppo in recent weeks in a battle separate to that with Daesh, and seek to completely recapture the city, Syria's largest before the war.