Syrian activists say 12 people have been killed and 100 wounded by government troops in the city of Homs.
On Monday activists said the regime appeared to be sending infantry reinforcements including tanks to Homs, with the aim of storming rebel-held neighbourhoods.
Mustafa Osso, a local activist, said residents were preparing for the expected assault and planned to fight "until the last person".
Pictures posted online showed the Babr Amr area of the city being shelled for a 17th day.
Members of the Syrian opposition have warned the government may intensify its attacks ahead of the February 26 referendum on a new constitution.
The referendum was announced by President Bashar al Assad as an apparent concession, but has already been dismissed as worthless by his opponents.
On Sunday, gunmen assassinated a prosecutor and a judge in the northwestern province of Idlib, an area largely controlled by the opposition. Read More