Members of Russian special forces are seen near a residential house where four suspected members of a militant group in Russia's volatile North Caucasus region were killed in a counter-terrorism operation, in St. Petersburg, Russia, August 17, 2016. REUTERS/Ilya Davlyatchin/Interpress

MOSCOW (Reuters) - Russian special forces troops killed four militants in a shoot-out at a flat in St. Petersburg on Wednesday in a counter-terrorism operation targeting gang leaders from Russia’s volatile North Caucasus region.

Russia’s National Anti-Terrorism Committee (NAC) said that three of the four men killed had been senior figures in the criminal underworld responsible for a string of terror attacks and attempted assassinations of police officers.

“Special forces from Russia’s FSB security service surrounded the bandits in a flat they were hiding in,” the NAC said in a statement. “When asked to lay down their weapons and give up they opened fire.”

Automatic weapons, ammunition, and several improvised explosive devices had been found in the flat, it said.

In a separate incident in the Moscow region, police said two men who had attacked a roadside police sentry point had been killed.

The attackers were originally from Central Asia and had carried out the attack wielding axes, it said.