Russia's Defense Ministry says one of its military jets has crashed while trying to land in southern Russia and the fate of its two crewmembers is unknown.

The ministry said the Su-24 bomber crashed Wednesday as it was approaching its base in the southern Volgograd region on a regular training mission. It said a search mission was underway to locate the crew.

The Russian air force has temporarily grounded its Su-24 fleet pending an investigation into the crash, according to a Defense Ministry statement carried by Russian news agencies.

The twin-engine Su-24 has been a mainstay of both the Soviet and Russian air force since the 1970s.