Russian state news agency TASS says it has not been able to confirm details of the weapon. But it quoted a source as saying: 'It will be possible to mount various nuclear charges on the "torpedo" of the Poseidon multipurpose seaborne system, with the thermonuclear single warhead similar to the Avangard charge to have the maximum capacity of up to 2 megatonnes in TNT equivalent.'

• Kremlin's Poseidon 'torpedo' sub is designed to destroy 'enemy navy bases' 
• Underwater drone to carry 2 megatonne nuclear warhead and travel at 70 knots
• In March, Putin boasted of nuclear weapons 'invulnerable to enemy interception'

Russia is developing an underwater drone that can carry a two megaton nuclear warhead capable of obliterating Western ports.

The Kremlin's Poseidon torpedo sub is designed to destroy 'enemy navy bases' and will be able to travel at up to 70 knots.

President Vladimir Putin announced plans for an underwater drone in his state-of-the-nation speech in March, in which he boasted of an array of new nuclear weapons 'invulnerable to enemy interception'. 

Russian state news agency TASS says it has not been able to confirm details of the weapon.

But it quoted a source as saying: 'It will be possible to mount various nuclear charges on the "torpedo" of the Poseidon multipurpose seaborne system, with the thermonuclear single warhead similar to the Avangard charge to have the maximum capacity of up to 2 megatonnes in TNT equivalent.'

CC:dailymail