MOSCOW - A new hypersonic nuclear missile that Russia says it has deployed is fueling concerns of a new arms race with the US as the clock ticks down on the expiry of the last treaty limiting the strategic arsenals of the two former Cold War foes.

Russia's first regiment of Avangard missiles was commissioned in the Urals region of Orenberg, Defense Minister Sergei Shoigu said Dec 27, days after President Vladimir Putin boasted that the new weapon could penetrate any defensive shield.

"Not a single country possesses hypersonic weapons, let alone continental-range hypersonic weapons," Mr Putin told military chiefs. "They're trying to catch up with us."

The Russian leader unveiled the Avangard and five other new-generation weapons in his annual state-of-the-nation address in March 2018, saying it could travel at up to 20 times the speed of sound like a "meteorite" or a "fireball".

The new weapon has gone into service amid heightened tensions between Moscow and Washington after President Donald Trump pulled the US out of a landmark 1987 treaty banning deployment of short- and medium-range missiles, accusing Russia of being in breach of its terms.

The Kremlin denied the allegation.

Russia and the US are also confronting each other over alleged Kremlin meddling in the 2016 presidential election, the conflicts in Ukraine and Syria, and Iran's nuclear programme.

The two sides are deadlocked over the future of the 2010 New START treaty that limits their nuclear arsenals and is due to expire in February 2021.

The Trump administration has so far rebuffed Russian calls to begin talks on extending the treaty, saying that any new accord should include China, which refuses to accept limits on its much smaller nuclear capability.

US experts visited a facility with Avangard missiles in November as part of a system of mutual inspections under the treaty.

The demise of New START "will have a disastrous impact" on the strategic balance between Russia and the US, said Alexander Golts, an independent defence analyst in Moscow.

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"We'll be going back to the period that led up to the Cuban missile crisis" in 1962, when the Soviet Union and the US came close to nuclear war, he said.

While the US alongside China is also developing hypersonic technology, it's probably "a couple of years" away from producing a weapon of such a calibre, Defense Secretary Mark Esper said in August.

The general who oversees US nuclear forces, Air Force Gen. John Hyten, said in February that hypersonic missiles can strike America within 15 minutes, half the time of ballistic weapons.

"This is an unprecedented situation in which we see that Russia is technologically ahead of the US and the Pentagon is playing catch up," said Nikolai Sokov, a senior fellow at the Vienna Center for Disarmament and Nonproliferation. "The U.S. only woke up this year to this technology and has started to throw money at it."

Russia successfully tested Avangard in December last year, firing it from a military base in the southern Urals 6,000km to the Kamchatka peninsula.

After a ballistic launch, the Avangard glides toward its target with a high degree of maneuverability.

The difference between the hypersonic weapon and a traditional ballistic missile is that it "disappears and we don't see it until the effect is delivered," Gen. Hyten said in testimony before the Senate Armed Services Committee.

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Claims the Avangard can evade any defences are overblown since it can be shot down in the early ballistic phase of its trajectory, said Mr Golts, the defence analyst.

The real breakthrough will come when Russia implements the same technology in another weapon class, like cruise missiles, according to Mr Sokov, the disarmament expert.

Abandoning New START at this juncture would be a major mistake, Democratic Senator Jeff Merkley warned this month.

There's bipartisan support in the US Congress for extending the agreement, which "has successfully kept the US and Russia out of a modern-day nuclear arms race," he said on Twitter. "We cannot risk unleashing a new Cold War."