The Intermediate-Range Nuclear Forces treaty, signed by the US and Russia more than 30 years ago to limit the deployment of medium-range nuclear missiles, may be living its last few days after President Donald Trump said he would "terminate it."
Trump's announcement was condemned by Russia and US allies alike as concerns of a new fully-fledged arms race between the two countries flare up.
Here's everything you need to know about the INF treaty.
What's the INF Treaty?
The Soviet Union achieved strategic parity with the US in the mid to late 1970s and started developing missiles that were more mobile, accurate, easily deployable and concealable and that could cover targets in Western Europe, North Africa, the Middle East but also Asia, Southeast Asia and the US state of Alaska.
They thus ushered in "what was perceived as a qualitative and quantitative change in the European security situation," according to the Intermediate-Range Nuclear Forces (INF) Treaty.
Signed in 1987 by Russia's Mikhail Gorbachev and America's Ronald Reagan, the INF Treaty required the US and Soviet Union to eliminate and permanently commit not to develop nuclear and conventional ground-launched ballistic and cruise missiles with ranges of 500 to 5,000 kilometres.
By June 1, 1991, the implementation deadline, the two countries had destroyed a combined total of 2,692 short-, medium-, and intermediate-range missiles.
Are there violations?
The US first raised concerns about a possible Russian violation of the treaty in 2014, and repeated such claims in subsequent years. It affirms that the country's 9M729 missile can fly more than 500 km.
NATO announced in December that allies had "identified a Russian missile system that raises serious concerns," urging Russia to engage in bilateral dialogue with the Alliance.
"Allies emphasise that a situation whereby the United States and other parties were abiding by the treaty and Russia were not – would be a grave and urgent concern," the NATO statement said.
On Saturday, US president Donald Trump ramped up tensions, telling reporters after a rally in Nevada: "We're going to terminate the agreement and we're going to pull out."
"Russia has violated the agreement. They've been violating it for many years," he said, adding: "I don't know why President Obama didn't negotiate or pull out."
Russia, which denies that it is in violation of the treaty, has also lobbed accusations at the US, arguing that the Aegis Ashore missile defence system activated in Romania and Poland is capable of firing long-range cruise missiles.
Sergey Ryabkov, Russia's deputy foreign minister, described Trump's announcement as a "very dangerous step" and called on "Washington to show a balanced and sober approach."
What withdrawing would mean?
"Some Russian politicians think that Russia would benefit from the US withdrawal from the agreement,"Alexander Golts, a Russian military analyst, told Euronews.
These politicians, Golts explained, believe Russia is at a disadvantage because other countries have intermediate-range missiles.
But the analyst also warned that it could be the beginning of a new arms race between the two countries in which, if the US accusations are true, "for the first couple of years, Russia would be ahead."
"As for a fully-fledged arms race, the withdrawal from the INF agreement is but a beginning: the New Start Treaty (preventing the development of strategic nuclear missile launchers) is also in danger.
"It might not happen right away but in some time we will be back to the situation in the 1980s when over 2,000 Soviet Pioneer missiles were capable of hitting Bonn, Paris, London but couldn't reach Washington or New York — and the American Pershing missiles could destroy Russia's most important cities within six-seven minutes.
"Thirty years on, if the INF is destroyed, we will be back to that," he said.