The explosion in the village of Dvani was followed by a second blast when a group of police arrived to help, wounding three more officers -- one seriously, Interior Ministry spokesman Shota Utiashvili said. He blamed Ossetian paramilitaries for the blast.
European Union monitors patrolling the area as part of the truce said the blast was caused by an "improvised explosive device" and was followed by gunfire.
Dvani is located near the strategic city of Gori, which was occupied by Russian forces following the brief war Moscow fought with Georgia in August.
Georgian police forces retook control of Gori and the surrounding regions after Russian troops withdrew to South Ossetian territory.
Around 200 EU monitors were deployed to the region as part of a cease-fire deal negotiated by Presidents Nicolas Sarkozy of France and Dmitry Medvedev of Russia following the withdrawal of Russian troops to South Ossetia and another breakaway region, Abkhazia.
"This attack by an improvised explosive device is an unacceptable breach of the Sarkozy-Medvedev agreement," the EU monitoring team said in a statement. "Today's attack risks escalating the still-tense situation along the administrative boundary lines. We repeat our call on all sides to prevent further provocations."
On Saturday, several dozen militants from South Ossetia entered the village of Perevi in Georgia, on the western border with South Ossetia. Georgian officials said the move was a blatant violation of the cease-fire, and EU observers warned that it could exacerbate tensions.
South Ossetia's separatist leader, Eduard Kokoity, said part of the village was located in the breakaway region and its forces entered it legally.
Georgian President Mikheil Saakashvili, meanwhile, vowed that Russian troops would never be allowed to remain in the country's territory.
"We will do everything not to yield to the provocations of their occupiers," Saakashvili said in televised comments Monday.
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