Shells and rockets crashed into Sunni Muslim districts of Homs that have already endured weeks of bombardment as Assad's forces, led by officers from his minority Alawite sect, try to stamp out an almost year-long revolt against his 11-year rule.
"Intense shelling started on Khalidiya, Ashira, Bayada, Baba Amro and the old city at dawn," opposition activist Mohammed al-Homsi told Reuters from the city on the Damascus-Aleppo highway.
"The army is firing from the main thoroughfares deep into alleyways and side streets. Initial reports indicate at least two people killed in the souk area," he said.
The London-based Syrian Observatory for Human Rights said later at least seven people had been killed by shellfire in Baba Amro. The accounts of opposition activists were echoed by those from other observers, including the Red Cross.
At least 59 civilians and soldiers were killed on Sunday in a violent backdrop to a referendum on a constitution that offers some reforms, but could enable Assad to keep power until 2028.