President Vladimir Putin said on Wednesday that Russia had successfully tested a Poseidon nuclear-powered super torpedo that military analysts say is capable of devastating coastal regions by triggering vast radioactive ocean swells.

As US President Donald Trump has toughened both his rhetoric and his stance on Russia, Putin has publicly flexed his nuclear muscles with the test of a new Burevestnik cruise missile on October 21 and nuclear launch drills on October 22.

There are few confirmed details about the Poseidon, named after the ancient Greek god of the sea, but it is essentially a nuclear-capable cross between a torpedo and a drone.

Putin, over tea and cakes at a hospital in Moscow with Russian soldiers wounded in the Ukraine war, said the test had taken place on Tuesday.

"For the first time, we managed not only to launch it with a launch engine from a carrier submarine, but also to launch the nuclear power unit on which this device passed a certain amount of time," Putin said.

"There is nothing like this," he said, adding there was no way to intercept the Poseidon, which analysts believe has a range of 10,000 km (6,200 miles) and can travel at about 185 km per hour.

The Burevestnik and Poseidon tests are intended to send a clear message that Russia, in Putin's words, will never bow to Western pressure over the war in Ukraine.

For Trump, who has called Russia a "paper tiger" for failing to swiftly subdue Ukraine, the message is that Russia remains a global military competitor, especially on nuclear weapons, and that Moscow's overtures on nuclear arms control should be acted on.

POSEIDON AND THE NEW NUCLEAR ARMS RACE

The Poseidon is a new weapon that has appeared amid what Putin has cast as a global arms race - primarily between the United States, Russia and China - to modernise and develop their nuclear arsenals.

Poseidon, known in NATO as Kanyon, is 20 metres long, 1.8 metres in diameter and weighs 100 tonnes, according to Russian media.

Arms control experts say the weapon breaks most of the traditional nuclear deterrence and classification rules. They have estimated it would carry a two megaton warhead and perhaps is powered with a liquid-metal-cooled reactor.

Putin said Poseidon's power exceeded that of "even our most promising Sarmat intercontinental-range missile", which is known as SS-X-29, or Satan II.

Since first announcing the Poseidon and Burevestnik in 2018, Putin has cast them as a response to US moves to build a missile defence shield after Washington in 2001 unilaterally withdrew from the 1972 Anti-Ballistic Missile Treaty as well as to NATO's eastern enlargement.

After Russia's test of the Burevestnik, Trump said Putin should end the war in Ukraine instead of testing a nuclear-powered missile.