Syrian government troops have unleashed a fresh assault on the city of Homs, ignoring Western pleas to halt the violence.
Amateur footage reportedly filmed on Thursday appears to show the Syrian military firing mortars and artillery.
Makeshift hospitals have been set up treat the wounded, but food and medical supplies are running out.
Residents of Homs have been quoted by activist websites as saying that electricity and water supplies have been cut off in many neighbourhoods.
Opposition groups say as many as 400 people have died in Homs alone over the past week.
Syrian authorities have not commented and it remains impossible to verify those figures.
Access to the country is tightly controlled and the movement of foreign journalists in Syria is heavily restricted.
Both the United States and Turkey are looking at ways to provide civilian aid.
But the world remains divided on how to deal with the 11-month uprising against President Bashar Assad’s rule.
Russia and China have opposed Western calls for Assad to step down.