"The army's continuous bombardment over the past 11 days has made the critical humanitarian situation in rebel areas of Homs even worse," Syrian Observatory for Human Rights director Rami Abdel Rahman told AFP.
"An unknown number of rebels and civilians wounded in recent days are dying from their injuries, because there is no medical equipment to treat them," he added.
Khaldiyeh and the Old City neighbourhoods of Homs have been under tight army siege for more than a year and since late June have come under steady shell and rocket fire as well as air strikes in a withering offensive by the regime.
Activists on the ground confirmed the shortage of medical care.
"The medical community in the besieged areas of Homs is suffering from shortages," said Homs-based activist Yazan.
Large quantities of medical supplies, Yazan told AFP via the Internet, had been used up due to the increased number of injuries caused by the shelling.
"This campaign on Homs has been the fiercest" since the start of the siege on the city's rebel areas more than a year ago, he added.
At the start of the revolt against President Bashar al-Assad in March 2011, Homs was dubbed "the capital of the revolution" when it was shaken by widespread protests calling for regime change.
Now, the rebels are caught in a small segment of the city, barely covering some two square kilometres (miles) in the centre.
Early today, the army shelled the rebel zones as fresh fighting erupted in the streets, said the Observatory.
More than 100,000 people have been killed in Syria's 27-month war, most of them civilians, says the group.
