STAVROPOL, August 19 (RIA Novosti) - The Federal Security Service (FSB) has information on the masterminds of a suicide bombing in southern Russia that left 24 dead and 136 injured, Russia's top investigator said on Wednesday.

"The FSB has received information about the organizers of the terrorist act," said Alexander Bastrykin, the head of the Investigations Committee of the Prosecutor General's Office.

He refused to name any of the suspects at this stage, but said they belonged to the same armed underground groups that had staged similar attacks in recent years.

A suicide bomber rammed an explosives-laden minivan into the gate of the police headquarters in Ingushetia's largest city, Nazran, on Monday.

Bastrykin told President Dmitry Medvedev that the Investigations Committee and the FSB would do all they could to solve the crime, which was the worst terrorist attack in the republic for several years.

Following the bombing, Medvedev sacked Ingushetia's interior minister and ordered a probe into police activities.

The explosion, estimated at equivalent to 400 kg of TNT, left a crater about 4 meters wide and 2 meters deep and triggered more explosions as ammunition detonated in the police headquarters. The blast shattered windows and smashed balconies in residential buildings, also destroying dozens of cars.

Ingushetia and the neighboring republics of Chechnya and Dagestan have seen a rise in militant violence in the past few months, with frequent attacks on federal troops, police and other officials.