The Syrian government says it is trying to evacuate civilians from the city of Homs, blaming rebel fighters for obstructing efforts to get people out safely.

Activists, however, say the army has intensified shelling of residential districts of Homs, the centre of the revolt against President Bashar al-Assad.

This amateur video said to be shot on June 18, which Reuters cannot independently verify, purports to show Syrian troops firing mortars in Homs.

The Syrian Observatory for Human Rights says around 1,000 families were surrounded in the city, under fire from the army and security forces.

They also said that dozens of wounded people were in danger because of a lack of medical equipment.

Sarah Sheffer, Reuters