Residents of the flashpoint city of Hama mobilized late Monday to deny Syrian President Bashar Assad's troops entry, the Associated Press reports.
Hama, where as many as 500,000 people took to the streets for a demonstration on Friday against Assad's regime, has been a focal point of opposition since the Syrian revolt erupted in mid-march.
Activists in Hama say a child was among six people shot dead by security forces since Monday.
"Tanks are now posted at access routes to the city except for the northern entrance," Rami Abdel Rahman, head of the London-based Syrian Observatory for Human Rights, told the AP by telephone.
"Residents have mobilized. They're prepared to die to defend the city if need be rather than allow the army to enter," Rahman said. "Residents have been sleeping on the streets and put up sand barriers and tires to block any assault."
Another activist, however, insisted that Hama 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.
Apart from the six killed - including 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.
Agents in their cars "shot in the air to terrorize residents," one resident said, while low-flying warplanes overflew the city emitting sonic booms.
There was no independent confirmation of the reports from activists as Syrian authorities have curbed foreign media coverage.
The violence is the first in Hama since security forces gunned down what is now believed to be 48 protesters in the city on June 3.
Hama was also the scene of a 1982 bloodbath in which an estimated 20,000 people were killed when the army crushed an Islamic revolt against the rule of the president's predecessor and late father, Hafez al-Assad.
Rights groups say that more than 1,300 civilians have been killed and 10,000 people arrested by security forces since mid-March.