The first explosion occurred at night on the border between North Ossetia and Ingushetia. A cargo train was blown up. The second blast was in Ingushetia's west in the morning near a court building.
The third explosive went off near a bus stop in Nazran, the biggest republican city, and the fourth hit western Ingushetia when a military column was passing.
The republic's Acting Interior Minister Bislan Khamkhoyev said the attacks were revenge to policemen who had recently conducted successful operations against several groups of local militants and added it would not stop his units.
"The detention of the remainder of the criminal groups is a matter of time," Khamkhoyev said.