He said the blast had almost totally destroyed the police headquarters in the town of Gori, 80km to the west of the capital Tbilisi.
"According to preliminary information, this was a terrorist act," said spokesman Guran Donadze.
About 10 people had been injured in the blast and several cars had been gutted.
Gori, hometown of the late Soviet leader Stalin, was the scene of some minor clashes after a mainly peaceful revolution a year ago when now-president Mikhail Saakashvili's supporters overthrew the government.
Gori is located in the west of Georgia, close to the breakaway
republic of South Ossetia, where Georgian troops have in the past clashed with separatist forces.
The status of South Ossetia remains a sensitive issue in Georgia. Saakashvili has vowed to bring it and other wayward regions of his country back under the control of the central government.
Interior Minister Ivane Merabishvili was rushing to the town, Donadze said.