Syrian opposition activists say government forces have launched a major offensive against rebel-held areas in the city of Homs.
They said jets and mortars had pounded rebel-held areas of the city that have been under siege by President Bashar al-Assad's troops for a year, and soldiers fought battles with rebel fighters in several districts.
Unverified video footage showed explosions and clouds of smoke rising from what the activists were rebel districts.
Syrian state media said the army was "achieving great progress" in the Khalidiyah district.
UK-based activist group the Syrian Observatory for Human Rights said violent clashes were taking place around the historic Khalid Ibn al-Walid mosque in Khalidiyah, which had earlier caught fire.
Three weeks ago Hezbollah spearheaded President Assad's recapture of the border town of Qusair, a former rebel bridgehead for smuggling in guns and fighters. Last week the rebels lost another border town, Tel Kalakh.
Reuters reports those gains have consolidated President Assad's control over a corridor of territory that runs from the capital Damascus through Homs to the traditional heartland of his minority Alawite sect in the mountains overlooking the Mediterranean.