Forces loyal to Syrian President Bashar Assad have unleashed their heaviest artillery barrage in a week to dislodge rebels from a strategic western town, according to activists.

Pro-Assad troops, including fighters from the Lebanese militia Hezbollah, launched an offensive against the rebel-held town of Qusair a week ago. They have gained ground, but rebels continue to hold some positions.

Local activist Hadi Abdullah and the British-based Syrian Observatory for Human Rights say the artillery barrage began early today. The regime wants to recapture Qusair to open a land corridor between its strongholds in the capital Damascus and on the Mediterranean coast.

The Qusair offensive has highlighted Hezbollah's growing role in Syria's civil war. Today's push comes ahead of a speech by Hezbollah chief Hassan Nasrallah, his first since the offensive began.