Armed groups fired Rocket- Propelled grenades (RPGs) at a civilian bus in central Hama province Wednesday, killing six people instantly, state-run SANA news agency reported Thursday.

The bus was targeted with two RPG rockets near the Shizar town in Hama's countryside, said SANA, adding that six passengers were killed instantly, while six others injured and were transported to nearby hospitals.

Hama, Syria's fourth-largest province, is one of the hotbeds of armed insurgency against the regime of Syrian President Bashar al- Assad.

Local and foreign reports said that al-Qaida fighters are sneaking from Iraq to Syria to join Sunni insurgents in their battle against the Damascus regime, which is dominated by a Shiite offshoot sect.

The Syrian government has accused some Arab and Western countries of providing weapons and financial support to the armed groups in Syria. It said in December 2011 that "armed terrorist groups" had killed more than 2,000 army and security personnel during the unrest.

The United Nations said recently that "well over" 7,500 people have died in Syria's violence.