A Russian missile launching off its own soil (Picture: Russian MOD).
Russian President Vladimir Putin has warned the US that if it walks out of a key arms treaty and starts developing banned missiles then Moscow will do the same.
Mr Putin's remarks to Russian news agencies came a day after US secretary of state Mike Pompeo announced at a NATO meeting that Washington will suspend its obligations under the Intermediate-Range Nuclear Forces Treaty (INF) in 60 days, citing Russian "cheating".
Russia has denied violating the treaty.
President Donald Trump earlier this year announced his decision to withdraw from the INF, which has been described as a cornerstone of global security, accusing Russia and China - which is not a signatory to the treaty - of violating it.
The INF is a deal signed in 1987 between Russia (then the USSR) and the United States to significantly cut the nuclear weapons capabilities of both sides around Europe.
INF stands for ‘Intermediate-Range Nuclear Forces Treaty’ which states: "Each Party shall eliminate its intermediate-range and shorter-range missiles, not have such systems thereafter, and carry out the other obligations set forth in this Treaty."
What weapons did it ban?
In simple terms, it stopped Moscow from having ground-based missiles that could hit Europe and stopped Washington basing missiles in Europe that could hit Russia.
Neither side was allowed any surface-launched missile that had a range of between 500 and 5500 km (310–3420 miles).
The US think tank the Arms Control Association says more than 2600 missiles were destroyed as a result of this treaty.
But what did it mean for the UK?
It significantly reduced the risk of the UK being hit by a nuclear strike at short notice. As a result, in the early 1990s, the 'four-minute-warning' public alert system ended operations.
The deal also meant an end to the American nuclear-armed cruise missiles that had been controversially based at RAF Greenham Common and RAF Molesworth.
This treaty had no effect on the UK’s own nuclear weapons capabilities or rights, as it was only between Russia and the US.
Why does US President Donald Trump want to pull out of the INF treaty?
It depends what happens after the treaty is scrapped, but the worry in much of Europe is a return to the days of the Cold War when Russia had thousands of missiles that could hit places like London, Paris and Berlin in a matter of minutes.
NATO says the INF treaty “has been crucial to Euro-Atlantic security and we remain fully committed to the preservation of this landmark arms control treaty”.
But the head of the alliance, Secretary General Jens Stoltenberg, has also said it is Russia that is jeopardising the treaty by developing new missiles.
'We don't want a nuclear arms race', says the NATO Secretary General
The UK’s Defence Secretary Gavin Williamson also told the Financial Times “we will be absolutely resolute with the United States in hammering home a clear message that Russia needs to respect the treaty obligation that it signed.”
However given that Europe directly benefitted, more than the US, from this treaty it’s likely the private conversations are trying to persuade America not to pull out, at least not without something better in place.
What is Russia's stance on it?
Russia denies breaching the INF treaty and says the 9M-729 missile fully complies with the INF treaty.
But it counter-accuses the US of breaching the treaty by placing a missile defence shield (effectively missiles designed to shoot down other missiles) in Europe, and with weapons carried on drones.
Russia's Deputy Foreign Minister Sergei Ryabkov warned withdrawing from the treaty would be a ‘dangerous step’ that could lead to a new arms race.
He told the RIA Novosti news agency that if the US did pull out of the INF treaty “we will have no choice but to undertake retaliatory measures, including involving military technology”.
Will President Trump pull out?
That’s not clear yet. Donald Trump may be using the threat of withdrawal as a piece of hardball negotiation, or he may be committed to it.
There’s also some debate in the US whether President Trump has the power to withdraw, or whether he has to have the backing of the Senate which ratified the treaty.
Then-President Ronald Reagan and General Secretary Mikhail Gorbachev speak after signing the INF treaty in 1987 (Pictures: Ronald Reagan Presidential Library).