On Thursday morning, police cornered the gunmen in a house in southwest Nazran. The subsequent shootout lasted for an hour and a half before the house was blown up by the occupants. Four police officers were killed and three injured in the operation.
"While cleaning the rubble, we found four 200-kilogram barrels filled with potassium nitrate and with detonators attached. The bomb could have exploded at any time," the spokesman for the Federal Security Service's Ingushetia department said.
Police also found firearms, ammunition, a car loaded with explosives and the body of an unidentified man.
Earlier reports said three militants, including one woman, died in the explosion, which had the force of the equivalent of 70 kilograms of TNT. Three nearby houses and a number of cars were damaged.
"The force of the explosion literally blew the two-story house where militants were surrounded into the air, and the shock wave leveled several houses," the source said.
A criminal case was launched. Investigators are currently working at the scene.
The Russia-based human rights group, the Moscow Helsinki Group, said in September that Ingushetia was on the verge of civil war as fighting between militants and authorities intensified. It also accused federal authorities of torture and abductions.