Syria's anti-government forces say they are intensifying their offensive to close in on the capital Damascus and topple the administration of President Bashar al-Assad.

The insurgents have taken control of the major northern city of Aleppo and the key central city of Hama since they stepped up their advance in late November.

The rebels are aiming to seize Homs, which is a key transportation hub in central Syria that leads up to Damascus.

The Syrian Observatory for Human Rights said on Saturday that local rebel factions had taken control of most of the country's southern areas while government troops have withdrawn from Daraa, Suwaidaa and Quneitra in the southwest.

CNN said on Friday that it obtained a statement by a group representing rebel forces in southern Syria, which said that their goal is to reach Damascus.

On Saturday, the rebels claimed to have advanced to within 20 kilometers from the southern gate of the capital.

The opposition forces have made major advances over the past few weeks, taking advantage of the conflicts in Lebanon and Ukraine.

The Lebanon-based Shia Muslim group Hezbollah and Russia have been providing military support to the Assad government.