Federal Security Service (FSB) forces are said to have begun a "large-scale" armed operation on Monday evening against militants "entrenched in a five-story building" in Neftekumsk, Russia's Stavropol region.
"Sounds of assault rifle fire and grenade explosions are coming from the vicinity of Kozlov Street," a Neftekumsk police source told Interfax .
A source in the Stavropol authority told Interfax: "The militants are entrenched in a five-story building, they are firing back from a window of one of the apartments."
"Operatives in law enforcement services located the militants as a result of preventive operations," the Stavropol source said.