Syrian President Bashar al-Assad's forces launched a major offensive on Saturday, June 29 against rebels in Homs, a centre of the two-year uprising, in their latest drive to secure an axis linking Damascus to the Mediterranean, Reuters said.

Activists said jets and mortars pounded rebel-held areas of the city which have been under siege by Assad's troops for a year, and soldiers fought battles with rebel fighters in several districts.

There were no immediate details on casualties but video uploaded by activists showed heavy explosions and white clouds of smoke rising from what they said were rebel districts. Loud, concentrated rounds of gunfire could also be heard.

Syrian state media said the army was "achieving great progress" in Khalidiyah neighborhood.

The attack on Homs city follows steady military gains by Assad's forces, backed by Lebanese Hezbollah militants, in provincial Homs villages and towns close to the Lebanese border.