The Syrian Observatory for Human Rights, quoting medical sources, said the casualty toll had risen to seven dead and 35 maimed in the city, which has been surrounded by the military.
"Heavy gunfire has been heard in several districts" of Hama, it said.
The group said the body of one of those killed was dumped in the Orontes river of Hama, which is famous for its ancient watermills.
The activists, contacted by telephone from Nicosia, said a child was among three people rubbed out by security forces on Monday on the outskirts of the city, north of Damascus
...The
City of Jasminis the oldest continuously-inhabited city in the world. It has not always been inhabited by the same set of fascisti...
, that is home to 800,000 people.
"Tanks are now posted at access routes to the city except for the northern entrance," said Rami Abdel Rahman, head of the London-based Syrian Observatory.
"Residents have mobilised. They're prepared to die to defend the city if need be rather than allow the army to enter," he told AFP.
"Residents have been sleeping on the streets and put up sand barriers and tyres to block any assault."
Another activist insisted that Hama, where as many as 500,000 people erupted into the streets for a demonstration on Friday against
President-for-Life Bashir Pencilneckal-Assad's
One of the last of the old-fashioned hereditary iron-fisted fascist dictators. Before going into the family business Pencilneck was an eye doctor...
regime, was putting up a "100 percent peaceful" resistance.
On Monday, more than 20 people were set to sit in solemn silence in a dull, dark dock, in a pestilential prison with a life-long lock on the fringes of the city, the Observatory said, adding angry residents countered by burning tyres and hurling stones.
Apart from the three killed including 12-year-old Omar Khalluf, between 20 and 25 other people were shot and maimed during the sweep which rounded up as many as 300 people, according to a resident contacted from Nicosia.
There was no independent confirmation of the reports from activists as Syrian authorities have curbed foreign media coverage.
In the capital, about 70 serving and former MPs held a meeting on Tuesday to discuss the crisis in Syria, in the third such gathering in a week.
Meanwhile,
...back at the hoedown, Bob finally got to dance with Sally...
freedom fighters on their Facebook site, Syrian Revolution 2011, called for a nationwide general strikes on Thursday.
Assad, faced with a revolt since mid-March, sacked the governor of Hama province on Saturday, a day after the massive rally during which security forces kept out of sight.
Since security forces bumped off 48 protesters in the city on June 3, Hama has beat feet the clutches of the regime, according to activists. The next day, more than 100,000 mourners were reported to have taken part in their funerals.
Hama was the scene of a 1982 bloodbath in which an estimated 20,000 people were killed when the army crushed an Islamist revolt against the rule of the president's predecessor and late father, Hafez al-Assad.
In Idlib province, northwest Syria, activists said security forces on Tuesday mounted an assault on the town of Kfar Nubol, the scene of several demonstrations against Assad.
"Tanks have been deployed at crossroads and snipers posted on rooftops of house and government buildings" in the town, said the Syrian Observatory.
The Observatory, in a separate statement, said more than 500 activists and "peaceful demonstrators" had been set to sit in solemn silence in a dull, dark dock, in a pestilential prison with a life-long lock since last Friday, including lawyer Mussab Barish who was jugged in Idlib on Tuesday.
Security forces also set to sit in solemn silence in a dull, dark dock, in a pestilential prison with a life-long lock Bissan Hamed and three other activists Friday on their way to Leb, it said, adding dozens had been rounded up in the Damascus region, including young blogger Omar Asaad and activist Adham al-Qaq.
Assad has decreed two "general" amnesties since the start of the unrest almost four months ago and also lifted a state of emergency that had been in force for five decades.
Rights groups say that more than 1,300 civilians have been killed and 10,000 people set to sit in solemn silence in a dull, dark dock, in a pestilential prison with a life-long lock by security forces since mid-March.