The separatists ambushed a patrol car belonging to local police in the provincial capital, Grozny, on Thursday, firing a direct hit with a grenade launcher, the regional branch of Russia's Interior Ministry said in a statement.
The attack killed seven police officers on the spot and wounded another one, who was hospitalised with grave shrapnel wounds.
Aljazeera's Russia correspondent reported a high-ranking officer was also in the car when the attack took place.
Attacks by separatist fighters are daily events in Chechnya, but it is rare for Russian officials to acknowledge their losses so quickly.
Mainly Muslim Chechnya has been devastated by war, which has dragged on for more than a decade.
Separatists fought Russian troops to a standstill in a 20-month war that ended in 1996.
Russia says it is stabilising the region, but still maintains close to 100,000 troops in Chechnya.