According to Rami Abdulrahman, director of the Syrian Observatory for Human Rights, reporting on the conflict, Fateh al-Sham appeared to believe that the rebels were providing coordinates for airstrikes recently launched against the former Al-Qaeda affiliate.
"It's an open war on the Nusra Front," Abdulrahman said, adding that the morning attack triggered further battles that continued Tuesday afternoon along the border between Idlib province, under control of Fateh al-Sham, and northern Aleppo province.
The ongoing conflict, between the jihadist group and other rebel forces, has increased, after Syrian government forces backed by Russian air power liberated Aleppo last month. In a statement, Jaish al-Mujahideen called for other factions to "stand as if they are one man" against Fateh al-Sham.
The truce has largely held since that time, although both sides have accused each other of violations.
The Nusra Front changed its name to Jabhat Fateh al-Sham after announcing in 2016 that it was severing its ties with al Qaeda. It is still listed internationally as a terrorist group.