Police in Russia’s republic of Daghestan say two police officers and four rebels were killed in clashes on May 14.
Police spokeswoman Fatina Ubaidatova said the clashes began when police forces came across armed militants while searching an apartment building in the city of Derbent.
Ubaidatova said the militants threw a grenade at the police and took a wounded officer hostage.
She said the police stormed the apartment after obtaining information that the wounded officer had died.
The Interfax news agency, citing unidentified law enforcement officials, said at least four militants were killed in the apartment.
Interfax said fire brigades were working on the scene as the apartment caught fire.
The Sunni extremist group Islamic State (IS) claimed its fighters were behind the attack.
Daghestan has become the epicenter of violence for militants seeking to establish an Islamic state in the North Caucasus.