MOSCOW ? Russian security forces Saturday killed four militants in a special operation in Russia's troubled southern region of Dagestan, officials said.

"Four militants, who showed armed resistance, were liquidated" in the clash in the Khasavurtovsky region of Dagestan, an official with the local branch of the Federal Security Service (FSB) told the Interfax news agency.

The official said that three of the dead had already been identified as known members of a local militant group planning attacks.

The militants had been surrounded in a private house and opened fire when they were asked to surrender, the reports said.

Dagestan and other regions of the Russian northern Caucasus have been the scene of regular deadly clashes in recent months between Islamist militants and security forces amid an escalating insurgency.