A Russian fighter jet Su-24 crashed near Volgograd prompting Moscow to suspend operations of all aircraft of the same model, as the fate of the pilots remains unknown.

The tactical bomber crashed about 7km away from the runway in Russia's southern city of Volgograd near the Marinovka airport.

An investigation has been initiated into the incident as Moscow has ordered that all the twin-engine frontline bomber be grounded.

"The flight was performed without combat ammunition load by experienced pilots who have more than 1,000 logged flight hours each," a statement from Russia's defence ministry said.

"On the order of the Chief of the General Staff of the Russian Armed Forces flights of the Su-24 planes are suspended until the causes of the accident are investigated."

There were two pilots on board the aircraft and search and rescue measures are under way.

The Russian defence ministry has drafted in a special commission to lead the probe. The aircraft model was developed during the Soviet Era and its modified versions are still active in several former Soviet states.