LONDON (Reuters) - Four decades ago, the United States deployed cruise and Pershing II nuclear missiles in Europe to counter Soviet SS-20s - a move that stoked Cold War tensions but led within years to a historic disarmament deal.
"We can be proud of planting this sapling, which may one day grow into a mighty tree of peace," Soviet leader Mikhail Gorbachev told US President Ronald Reagan in December 1987 as they agreed to dismantle the rival systems under a treaty that scrapped all ground-based shorter-range and intermediate-range (INF) nuclear and conventional weapons - those with ranges between 500 km and 5,500 km.
The sapling survived until 2019 when Donald Trump, then US president, quit the treaty, citing alleged violations that Russia denied. But the risky implications of the pact's full unravelling are becoming fully apparent only now, as both sides set out their plans for new deployments.
On June 28, President Vladimir Putin said publicly that Russia would resume producing short and intermediate-range land-based missiles - something the West suspects it was already doing anyway - and take decisions on where to place them if needed.
Security experts assume these missiles, like most Russian systems, will be capable of carrying either conventional or nuclear warheads.
On July 10, the United States said it will start deployment in Germany from 2026 of weapons that will include SM-6s and Tomahawks, previously placed mainly on ships, and new hypersonic missiles.
These are conventional systems but some could also, in theory, be fitted with nuclear tips, and security experts said Russian planning would have to allow for that possibility.
The decisions, taken against the background of acute tensions over Russia's war in Ukraine and what the West sees as threatening nuclear rhetoric from Putin, add to an already complex array of threats for both sides. They also form part of a wider INF arms race with China.
"The reality is that both Russia and the United States are taking steps that they believe enhance their security, regardless of whether it comes at the expense of the other," said Jon Wolfsthal, director of global risk at the Federation of American Scientists.
"And as a result, every move that the United States or Russia make puts pressure on the adversary to respond in some way, politically or military. That's the definition of an arms race," Wolfsthal, a former US arms control official, said in a telephone interview.
STRIKE SCENARIOS
Andrey Baklitskiy, senior researcher at the United Nations Institute for Disarmament Research, said the planned deployments created "more scenarios for direct military confrontation between Russia and NATO countries" for which all sides needed to prepare.
Hypothetically, he said, these could include eventualities such as a Russian strike on a Polish base where Western weapons bound for Ukraine were being stored, or a US attack on a Russian radar or a command and control post.
He said each side already has the capability to carry out such strikes using sea- or air-launched missiles, but adding ground-based weapons would give them more options to conduct an attack and withstand the enemy's response.
The risk, the experts said, is that this fuels already-high tensions and prompts a further spiral of escalation.
Wolfsthal said he saw the planned US deployments in Germany as a signal of reassurance to European allies rather than a step conferring any significant military advantage.
"My only concern about the deployment of these systems is they may not really add to our military capability but they almost certainly add to the risk that a crisis could accelerate and grow out of control," he said.
Ulrich Kuehn, an arms control specialist at the Institute for Peace Research and Security Policy in Hamburg, said in a telephone interview: "From a Russian perspective, if you deploy these kind of weapons in Europe, they can generate strategic (threat) effects - to Russian command centres, to political centres in Russia, to airfields, airstrips where Russian strategic bombers are placed."
Russia might respond, he said, by deploying more strategic missiles that point at the continental United States.
HOW WOULD CHINA RESPOND?
Any deployment of Russian and US intermediate-range missiles could also prompt a further build-up by China, which was not bound by the 1987 Soviet-US treaty and so has been free to ramp up its own INF arsenal.
The US Department of Defense said in a 2023 report to Congress that China's rocket force has 2,300 missiles with ranges between 300 km and 3,000 km, and a further 500 that can travel between 3,000 km and 5,500 km.
Concern about China's missiles was an important factor behind Trump's decision to quit the treaty with Russia, and the US has already taken an initial step towards placing its own intermediate-range weapons in allied countries in Asia.
In April it made its first overseas deployment of previously banned ground-launched missiles when it took part in a two-week military exercise in the Philippines.
"This will not be a two-party arms race between Russia and the United States and its allies, it will be a much more complex one," Kuehn said, with potential to involve China and other US allies in Asia such as South Korea and Japan.
All three experts said the chances of Russia and the United States arriving at a breakthrough arms control deal of the kind that Reagan and Gorbachev struck in 1980s were remote.
"Even if Russia and the United States would totally agree that 'this whole thing is not helping anybody, let's get back to the INF treaty' or whatever, the US would not be able to do that because of China, because they really need those systems to match Chinese capabilities," Baklitskiy said.
The likelihood, he added, was that "we will just continue piling up those systems and targeting them at each other. So it doesn't seem like we have a nice time ahead of us."