A key Vladimir Putin ally has threatened to unleash nuclear armageddon on the West, as tensions continue to soar between Washington and Moscow.

His warnings come as Joe Biden comes under increasing pressure to allow direct NATO intervention in Ukraine.

Dmitry Medvedev is a Kremlin apparatchik whose political fortunes have been closely tied to those of Vladimir Putin.

He started his political career as a humble secretary for Putin during his time at the Mayor's office in Saint Petersburg in the early 1990s, before becoming President of Russia in 2008.

Medvedev served just one term, before stepping aside to allow his former boss to take up the reins of Russia once again.

He has repeatedly backed Putin's war in Ukraine and has on numerous occasions warned the West that Russia will not hesitate to use its nuclear weapons.

In a new interview with the state media outlet RT, Medvedev once again resorted to nuclear saber rattling, accusing the West of not taking Russia's red lines seriously.

He noted that US diplomats hardly wanted a World War 3, but for some reason, they believed "that the Russians will never cross a certain line."

He said: "They are mistaken. If it comes to the existence of our state, which the president of our country has repeatedly said, your humble servant has said, others have said, naturally, we simply will not have any choice.

"Every person who assumes the post of president of a nuclear country, he, in essence, takes on this obligation - to defend the country to the last. This also applies to the Russian Federation."

Medvedev added: "The current political establishment - both in the US and in Europe - lacks the insight and subtlety of mind that, for example, the same [Henry] Kissinger had."

His remarks come in the wake calls by US politicians to allow Poland to shoot down Russian missiles over Ukraine.

Republican Joe Wilson and the Democrat Steve Cohen, co-chairs of the Commission on Security and Cooperation in Europe, urged the US President to act decisively and without fear.

“Despite Russia’s continued escalation through hybrid warfare — airspace violations, attacks on critical infrastructure, and efforts to destabilise democratic institutions — we have hesitated to confront these threats decisively, allowing Russia to wage a war against the alliance with minimal consequences,” they wrote in a letter to Biden.

“In this context, Poland’s request to intercept and neutralise missiles over Ukraine is both necessary and urgent as a support mechanism for Ukraine and a safeguard to the frontline of NATO’s borders."