Syrian troops backed by fighters from the Lebanese Hezbollah movement pressed an offensive Monday to retake the strategic border town of Qusair amid reports of heavy casualties on both sides.

The Britain-based Syrian Observatory for Human Rights said more than 90 people have been killed since forces loyal to President Bashar al-Assad launched their attack on the rebel stronghold overnight Saturday. Among them were 23 members of Hezbollah, an armed Shiite militant group whose fighters have been playing an increasingly visible role in the battles underway in the area in recent weeks.

There was no immediate comment from Hezbollah, which has portrayed its involvement in the fighting around Qusair as an effort to defend Shiites living in a string of villages along the border. But there were reports that a number of funerals were being held in northern Lebanese villages for fighters killed in the offensive.

The town of Qusair, which has been under rebel control for more than a year, is apparently home to two competing weapon supply lines, and carries a great deal of strategic significant in the ongoing Syrian civil war. Recapturing the town would also be a major morale boost for those loyal to Syrian President Bashar al-Assad, and cut rebel forces off from one of their most important supply lines.