Russian FSB and National Guard forces have conducted a special operation against suspected North Caucasus militants in a residential building in St. Petersburg.

Russian FSB and National Guard forces have conducted a special operation against suspected North Caucasus militants in a residential building in St. Petersburg. Witnesses said they heard at least two explosions and shooting in the building, RT reported.

Photos on social media show dozens of police cars and heavily-armed officers around the building.

An official from Federal Security Service told RIA Novosti the agency is conducting an operation to detain suspected North Caucasus militants.

The operation is underway in an apartment block “to detain individuals who are on a federal wanted list and are accused of taking part in illegal armed gangs in the North Caucasus region,” the local FSB press service said, as cited by TASS.

People claiming to be witnesses have reported on social media of shooting which took place in the building.

At least three alleged fighters have been detained during the operation, RIA Novosti cited law enforcement sources.

The operation reportedly lasted some four hours. The officers collected several white cardboard boxes and left, RIA Novosti reported.