Attackers opened fire on Tuesday on a minibus carrying security forces in warring Chechnya, and then set off a bomb when a second vehicle came to help, regional officials said.
The region's pro-Moscow administration said the explosion took place in the Znamenskoye settlement, about 60km northwest of the regional capital Grozny.
Interfax news agency quoted a top Chechen Interior Ministry official, Akhmed Dakayev, as saying that three civilians had been killed, including two teenagers aged 13 and 14.
Chechen Interior Minister Ruslan Alkhanov said the bomb was equivalent to eight kg of TNT, according to ITAR-Tass.
Moscow has been trying for years to crush separatist violence in Chechnya.
Russian troops and other pro-Moscow forces control most of the territory and in March killed separatist leader Aslan Maskhadov.
But isolated attacks have continued and even spread beyond Chechnya's borders to the neighbouring regions.
President Vladimir Putin last week visited the Dagestan region, which neighbours Chechnya, where he called on ministers and commanders to double their efforts to stop the violence.