Clashes between militants and the Lebanese army continued for a third day in the north of the country.
The violence erupted after troops raided a militant hideout in the region, with fighting since then concentrated on Lebanon's second city of Tripoli.
The al-Nusra front, linked to al-Qaeda and Isis, warned the forces to halt their operations to clear areas occupied by the militants, and threatened to execute captive soldiers.
"We warn the Lebanese army against any military escalation targeting Sunnis in Tripoli," the group said in a statement quoted by AFP news agency.
"We call on it to lift its siege and accept a peaceful solution, or else we will be forced in the coming hours to bring closure to the issue of the soldiers we are holding hostage, given that they are prisoners of war."
According to Reuters, 10 soldiers and 12 militants had been killed in fighting up to Sunday.
Seven civilians are also reported to have been killed according to security forces.