In recent weeks, there were four incidents of fire coming from Syria and straying across the ceasefire line.
Last week, projectiles from Syria hit Mount Hermon, causing the popular site on the Israeli-occupied Golan to close down to visitors.
Israel, which is technically at war with Syria, seized 1,200km2 of the strategic Golan Heights during the 1967 Six-Day War, which it later annexed, a move never recognized by the international community.
Syrian opposition sources and state media gave differing accounts of Sunday’s clashes in Qusair, long used by rebels as a supply route from Lebanon to the provincial capital Homs.
Hezbollah has not commented, but in Lebanon’s Bekaa Valley on Monday several funeral processions could be seen. Pictures of dead fighters were plastered on to cars and mourners waved yellow Hezbollah flags.
Several ambulances were seen on the main Bekaa Valley highway and residents said hospitals had appealed for blood to treat the wounded brought back to Lebanon.
The air and tank assault on the strategic town of 30,000 people appeared to be part of a campaign by al-Assad’s forces to consolidate their grip on Damascus and secure links between the capital and government strongholds in the Alawite coastal heartland via the contested central city of Homs.
The government campaign has coincided with efforts by the US and Russia, despite their differences on Syria, to organize peace talks to end a conflict now in its third year and in which more than 80,000 people have been killed.
A total of 100 combatants from both sides were killed in Sunday’s offensive, according to opposition sources.