Moscow, Russia (CNN) -- A suicide bomber killed two officers and wounded four others outside a police station in the Russian republic of Ingushetia Monday, authorities said.
An hour later, a car bomb went off near the site of the first attack in the town of Karabulak. The Interior Ministry said at first that no one was hurt, but the Investigation Committee of the Russian Prosecutor's Office in Moscow told CNN later that the second car bomb hurt seven police officers and a civilian; none of the injuries were considered life-threatening.
Police believe the car belonged to the suicide bomber and that the second explosion was from a timed device or was remotely detonated.
In the first blast, a male suicide bomber rushed toward a car carrying police officers as the vehicle drove into the courtyard of the local police station, Russian authorities said. Six policemen were injured and two later died at a hospital, authorities said. The attacker died in the explosion.
The second explosion occurred when a car parked outside the police station blew up, authorities said.
The blasts in Karabulak, about 12 miles (20 km) from the regional capital Magas, follows the March 29 attacks in Moscow, where two female suicide bombers killed at least 40 people and wounded more than 60 others.
Since then, Russia -- especially the North Caucasus region -- has been hit by other attacks, including an explosion Sunday that derailed a train and is being investigated as an act of terrorism.
Chechen rebels claimed responsibility for the Moscow attack.
In recent years, radical Islamist rebels who are fighting against Moscow rule in the North Caucasus have broadened their insurgency to the republics of Dagestan and Ingushetia to bring instability to the entire region, analysts say.
Rebels say the upsurge in attacks is a retribution for the Kremlin's violence and arbitrary rule in the region, and promised "new acts of vengeance" in Russia.