NALCHIK, May 28 (RIA Novosti) - Four militants, holed up in an apartment, were killed during a special operation in Nalchik, capital of Russia's southern republic of Kabardino-Balkaria, on Thursday, a police official said citing preliminary reports.

"The number of gunmen and their identities will be established when the apartment has been searched," the source said adding that police were searching the premises for explosives.

At least four gunmen were earlier reported to have barricaded themselves inside an apartment after offering armed resistance to police who tried to arrest them.

In 2005, militants believed to be linked to Chechnya's separatists staged an assault on Nalchik targeting the city's main army, police and security bodies. Some 140 people, both militants and security officers, were killed in the attacks, official reports said.