Syrian fighter jets and artillery units pounded rebel-held areas of the central city of Homs on Saturday, in what activists described as the fiercest push to take full control of the city in more than a year.

The bombardment of districts including al-Qusoor, Khalidiya, Jouret al-Shayah and the ancient Old City began about 9am and continued for three hours before the army deployed ground troops.

The government has been pressing a campaign against pockets of resistance in central Syria since taking control earlier this month of the town of Qusair, which lies between Homs and the Lebanese border. Once known as the capital of the revolution for its early role in the uprising against President Bashar al-Assad, Homs is divided between government-controlled and rebel-held areas, which have been under siege for the past year.

''It's the worst day since the beginning of the siege,'' said Abu Rami, a spokesman for the opposition Syrian Revolution General Commission and a resident of al-Qusoor who uses a pseudonym. ''Civilians can't leave. We are trapped.'' He said five air strikes had accompanied heavy shelling from tanks on Saturday morning before the army and militiamen from the paramilitary National Defence Forces mounted an offensive.