Forces loyal to the Syrian government have reportedly killed dozens of rebels who were trying to break an army siege of parts of Homs, in central Syria, BBC News reported.

State-owned news agency Sana said troops killed 37 "terrorists" in one operation alone and several others in other attacks.

UK-based activist group the Syrian Observatory for Human Rights said at least 45 rebels were killed.

Syria's civil war has left at least 100,000 people dead.

The army's siege of rebel-held areas in Homs's Old City has lasted more than a year.

Observatory director Rami Abdel Rahman said the number of dead could be higher.

"They were killed as they tried to launch an operation to end the siege of Homs. They were ambushed by regime forces near the Khaldiya neighbourhood, which is under government control," he told AFP news agency.

Several thousand civilians are believed to be trapped by the siege.

In October, activists reported severe food and energy shortages in the besieged areas and warned that residents faced starvation.