The residents of Hama have mobilised to keep out the army from the flashpoint city which has become a centre of the anti-regime revolt in Syria, activists said on Tuesday.
The activists, contacted by telephone, said a child was among three people shot dead by security forces on Monday in districts on the outskirts of the city north of Damascus 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 for Human Rights.
"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 took to the streets for a demonstration on Friday against President Bashar al-Assad's regime, was putting up a "100 percent peaceful" resistance.
"The regime will have to think twice before launching a military operation in the city," he said, on condition of anonymity.
On Tuesday, more than 20 people were arrested on the fringes of the city, the Syrian Observatory said, adding that angry residents countered by burning tyres and hurling stones.
Apart from the three killed, who included 12-year-old Omar Khalluf, between 20 and 25 other people were shot and wounded during the sweep which rounded up as many as 300 people, according to a resident contacted by telephone from Nicosia.
Agents in their cars "shot in the air to terrorise residents," one resident said, while warplanes flew over the city emitting sonic booms.
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.