An explosion rocked an area on the peripheries of the eastern border town of Arsal on Tuesday, state-run National News Agency reported.
Media reports said the blast resulted from the accidental detonation of an explosive device that members of the jihadist group Fateh al-Sham Front were preparing in the the Khirbet Younin area in Arsal's outskirts.
The explosion killed Fateh al-Sham's bomb maker Abu Qassem al-Talli and seriously wounded his assistant Ahmed Abu Daoud, NNA reported later.
Militants from Fateh al-Sham and the rival jihadist group Islamic State are entrenched in rugged mountains along the Lebanese-Syrian border.
The Lebanese army regularly shells their positions while Hizbullah and the Syrian army have engaged in clashes with them on the Syrian side of the border.
The two groups overran the town of Arsal in 2014 and engaged in deadly battles with the Lebanese army for several days.