Thousands of civilians are believed to be trapped in Syria's central city of Homs, as government forces continue their heavy bombardment of the city, the UN said.<br /><br />Both government forces and opposition fighters appeared to be digging in, preventing residents from accessing food and medicine.<br /><br />UN humanitarian officials say they are providing food to half a million people in Syria, but not in Homs, which means many there are desperate for food, clean water and medical help.<br /><br />Al Jazeera's Jane Arraf reports.
