Syria's main opposition group is urging rebels to come from around the country to reinforce Qusair, a western town under attack by Syrian troops and members of Lebanon's Hezbollah group.

George Sabra, the acting chief of the Syrian National Coalition, says in a statement that "forces from outside Syria" aim to destroy Qusair and that rebels should "rescue" it.

Government troops were trying for a fourth day Wednesday to wrest control of Qusair from rebels. The town lies near the Lebanese border on land corridor linking the capital Damascus with the Mediterranean coast.

Rami Abdul-Rahman, who heads the Britain-based Syrian Observatory for Human Rights, said the government and Hezbollah bombarded Qusair with rocket launchers.

Hezbollah has held funerals for fighters whom officials close to the group say died at Qusair.