Communications were cut to the area around Jisr al-Shughour and the details of the attack were impossible to verify, but there have been unconfirmed reports in the past by residents and activists of Syrians fighting back against security forces.
The government promised a "decisive" response, setting the stage for an even stronger government crackdown against a popular uprising that began in mid-March and poses the most potent threat in years to the 40-year regime of the Assad family.
"We will deal strongly and decisively, and according to the law, and we will not be silent about any armed attack that targets the security of the state and its citizens," said Interior Minister Ibrahim Shaar.
Jisr al-Shughour, near the Turkish border, has been the latest focus of Syria's military, whose nationwide crackdown on the revolt has left more than 1,200 Syrians dead, activists say.
The town was a stronghold of the country's banned Muslim Brotherhood in the 1980s. Human rights groups said at least 42 civilians have been killed there since Saturday.