Rescue personnel work at the crash site of the Su-24 bomber in southern Russia, Feb 11, 2015. [Photo/IC]

MOSCOW - A Russian military jet crashed Wednesday while trying to land in southern Russia and the fate of its two crewmembers is unknown, the Defense Ministry said.

The ministry said the Su-24 bomber went down as it was approaching its base in the southern Volgograd region on a regular training mission. It said the plane carried no weapons when it crashed.

Efforts to locate the crew have been unsuccessful. The state RIA Novosti news agency said the plane left a deep crater when it slammed into the ground, and that rescue workers were still working to dig out the plane's nose section with the cockpit.

The base is located 870 kilometers (540 miles) south of Moscow and 270 kilometers (170 miles) east of the border with Ukraine.

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 the Russian air force since the 1970s.