A statement issued in the name of the U.S.-backed group, known as Division 30, said its fighters prevented Nusra Front gunmen from storming their head office.
The Britain-based Syrian Observatory for Human Rights said Friday’s fighting was concentrated south of the Syrian town of Azaz on the border with Turkey.
The group added that warplanes believed to be from the U.S.-led coalition attacked Nusra Front positions in the area.
Nusra Front’s attack came two days after the extremists abducted the leader of Division 30 and seven of his men.
Division 30 said five of its fighters were killed and 18 were wounded.