Syrian government forces and the Lebanese guerrilla group Hezbollah launched a fierce campaign to seize more rebel territory in the border town of Qusair on Saturday, May 25, sources on both sides of the conflict said, according to Reuters.

Rebels fighting to topple President Bashar al-Assad said additional tanks and artillery had been deployed around opposition-held territory in Qusair, a Syrian town close to the Lebanese border.

Rebels are largely surrounded in Qusair, a town of 30,000 that has become a strategic battleground. Assad's forces want to take the area to secure a route between the capital Damascus and his stronghold on the Mediterranean coast, effectively dividing rebel-held territories in the north and south.

Assad's forces are believed to have seized about two-thirds of Qusair, but the price has been high and rebels insist they are preventing any further advances.

The fighting in Qusair has also highlighted the increasingly sectarian tone of Syria's political struggle.

Syria's Sunni Muslim majority has led the struggle to topple Assad, and has been joined by Islamist fighters across the region, some of them linked to the militant group al Qaeda.