A Russian fighter jet has crashed during a training mission off the country's Pacific coast and the fate of its two crew members was not immediately known.

The Russian military said that the MiG-31 fell into the Avacha Bay on the southeastern coast of the Kamchatka Peninsula on Tuesday.

It said that rescue teams were searching for its two crew members.

The military said the aircraft was not carrying weapons. It did not immediately offer any further details or say what may have caused the crash.

The MiG-31 is a twin-engine, two-seat supersonic fighter designed to intercept enemy planes and cruise missiles at long ranges.

It has been in service with the Soviet and Russian air forces since the 1980s.

Another MiG-31 crashed in the Murmansk region in the Arctic in April and its crew members bailed out safely.

The Russian air force has suffered a string of crashes that some observers have attributed to a higher number of flights amid the fighting in Ukraine and tensions with the West.