"If US forces, Nato forces, are, were, in the Crimea, in eastern Ukraine, Russia is undefendable militarily in case of conflict, without using nuclear weapons in the early stage of the conflict,” Vyacheslav Alekseyevich Nikonov told a global security forum in Slovakia.
Mr Nikonov, who has served on the staff of Mikhail Gorbachev, Boris Yeltsin and Vladimir Putin, said that he had heard this at some point "from the Russian military", according to Defense One.
He was speaking the GLOBSEC Bratislava Global Security Forum.
The politician added that the west was “not just a force for good”, and said he was concerned about the lack of dialogue between Russia and the US and its allies to find a political solution.
His comments come after Russia’s Deputy Defence Minister Yuri Borisov said the country would upgrade its rocket artillery brigades by 2020 and President Vladimir Putin unveiled a futuristic new tank which is invisible to missiles and capable of annihilating targets more than five miles away.
In a move which angered the US and its Nato allies, Russia annexed Crimea during a period of political upheaval in Ukraine in 2014, claiming the instability threatened the interests of Moscow and the large ethnic Russian community living in Crimea.
Russia’s continued control of Crimea and support for separatist militants in neighbouring eastern Ukraine has continued to anger Washington and Nato.
Moscow refutes the “annexation” label following a disputed referendum which it claimed showed a majority of voters favoured separation from Ukraine. The UN General Assembly rejected the legitimacy of both the vote and the annexation, while the other members of the then G8 suspended Russia and imposed sanctions.
Both Russia and Nato have built up their military across shared borders since the annexation, with both sides accusing the other of aggression. Mr Nikonov cited 400 points of Nato military installations near its borders, some armed with nuclear weapons.
Moscow is believed to have the largest stockpile of nuclear weapons in the world with at least 7,300 in its possession, while the US ranks second globally with around 7,000.
Both countries have greatly reduced their nuclear arsenals since the Cold War but each retains far more weapons than any other country.
Both nations have a policy of “launch under attack”, which means they will not rule out launching their nuclear arsenal if faced with an existential threat.
The Military Doctrine of Russia, last updated in 2014, says Moscow reserves “the right to use nuclear weapons in response to the use of nuclear and other types of weapons of mass destruction against it and/or its allies, as well as in the event of aggression against the Russian Federation with the use of conventional weapons when the very existence of the state is in jeopardy.”
Although President Donald Trump has faced much criticism over his alleged links to Russia, US sanctions against the country remain in place over Crimea.
After Mr Trump’s initial overtures to Mr Putin, relations between Washington and Moscow have become more strained in recent weeks, with the White House reiterating America's demand that Russia withdraws from Crimea.
Mr Nikonov said is worrying that US officials have been fired for talking to their Russian counterparts as this could cause relations between the superpowers to deteriorate further.
The Pentagon this week successfully simulated the shoot-down of a hostile long-range ballistic missile launch in the first ever live test of its kind, seen as a warning to hostile regimes such as North Korea and Iran but widely noted in the world media, including Russia.
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