MOSCOW: A Russian military plane crashed into the sea during a training exercise in Russia's Far East region, leaving all 11 crew members missing and presumed dead, officials said on Saturday.

The Tupolev Tu-142 plane disappeared from radar as it was coming to the end of a training mission on Friday over the Tatarski Strait that divides Russia's Far East island of Sakhalin from the mainland, the defence ministry said.

"Given the conditions under which the catastrophe took place, we can presume that all the crew aboard the Tu-142 were killed," a source in the emergencies ministry told the RIA Novosti news agency.

"But search operations will continue as long as there is the slightest hope of finding someone alive," the official added.

Military sources told Russian news agencies there were 11 crew aboard the plane and state media published their names in full.

An emergencies ministry source in the Khabarovsk region in the Far East told RIA Novosti that in the early morning an object was found at a depth of 44 metres (144 feet) underwater "which appears to be the fuselage of the plane".

"Objects are being investigated at water level which could be fragments of the plane," the source added. State television showed small scraps of material recovered and believed to have come from the doomed plane.

Search teams led by Russia's Pacific Fleet were searching for the plane's black boxes and could use special submersibles to locate them, RIA Novosti said.

However the type of black boxes used on the plane can only keep information in salt water for 36 hours, posing a major obstacle to the investigation if they are not found rapidly, RIA Novosti said.

Officials said the most likely cause of the crash was a technical failure.

"Based on the information we have in hand now, a mechanical fault is viewed as the priority theory," a source close to the investigation told the Interfax news agency.

Investigators have opened a criminal enquiry into the possible infringement of flight rules and preparation, a spokesman for the investigative committee of prosecutors for the Khabarovsk region told state television.

All flights by the air force of the Russian Pacific Fleet have been suspended pending the results of an investigation into the accident, Russian news agencies said.

Deadly accidents are a frequent occurrence in Russia's armed forces whose military hardware still includes ageing Soviet-era equipment.

The decorated commander of the country's celebrated military aerobatic stunt team, the Russian Knights, was killed in August when two Sukhoi Su-27 fighters collided in practice for the annual air show.

The Tu-142 is a reconnaissance anti-submarine warfare jet which was first introduced into the armed forces in 1971. Some 75 Tu-142 jets are currently employed by the Russian armed forces, the ITAR-TASS news agency said.