At least four policemen were killed when a car laden with explosives blew up Friday at about 7.15 p.m. Moscow time (3.15 p.m. GMT) in downtown Nazran with the force of 20 kilograms of TNT.
"There are two main theories we are working on. It is not ruled out that the crime was directed against police. The second theory is destabilization of the situation in the republic," Yury Turygin said.
The bomb went off when the officers were examining the Lada car, parked near a community center, a police source said, adding that militants may have planned for the car to blow up on Saturday, when events to celebrate Russia's Day of Knowledge were to be held at the center.
"Police had received a telephone call about a suspicious car. The vehicle exploded when the officers arrived at the scene," he said.
A spokesman for the Ingush Prosecutor's Office said a criminal case had been launched, and that investigators consider the blast to be a terrorist attack.
The volatile province has seen a surge in militant attacks against police and civilians in recent months. Neighboring Chechnya saw two Moscow-led military campaigns against separatist regimes in the 1990s- early 2000s.
Earlier Friday, a teacher's family was gunned down in Ingushetia, when gunmen broke into their house.
