A military helicopter crashed Saturday in Russia's North Caucasus republic of Dagestan, killing all three people onboard, the Defense Ministry said.

The Air Force Mi-35 helicopter crashed into a mountain while flying in poor weather conditions, said Defense Ministry spokesman Igor Konashenko

The helicopter disappeared from radar at 14:30 Moscow time (1030 GMT), and local residents reported hearing a crash about 15:00 (1100 GMT), Konashenko said.

"Reports from the crash site said that three members of the Mi-35 crew

died," the spokesman said, adding that rescuers were on their way to the scene.

The Mi-35 was guarding an army column moving through the area, the ministry said.

Heavy fog and poor visibility in the area made it difficult for rescuers to reach the site, local media reported.

Defense Minister Anatoly Serdyukov has ordered an investigation of the crash and all Mi-35 helicopters have been grounded pending the probe's outcome, Konashenko said.

Prosecutors in Russia's Southern Military District have opened a criminal probe into the crash, said the office of Russia's chief military prosecutor.

The Mi-35 is an advanced version of the Mi-24, a large helicopter gunship that can be used for attacking armored vehicles, providing fire support for ground forces and transporting servicemen and cargo.