Russia's top investigative body says four suspected militants have been killed in a shoot-out with intelligence officers in St. Petersburg.

The Investigative Committee said in a statement on Wednesday FSB officers were raiding apartments in Russia's second-largest city looking for suspected Islamic insurgents who have fought in Russia's North Caucasus.

The investigators said the suspects holed up in an apartment block on the outskirts of St. Petersburg and opened fire when the officers tried to detain them. No civilian or FSB casualties have been reported.

Television footage from the scene showed FSB officers in riot gear surrounding the sprawling apartment block.

Shoot-outs between police and suspected Islamic militants are common in Dagestan, Russia's hotbed of Islamic insurgency, but the violence rarely spills outside the North Caucasus.