Russia is in violation of a landmark Cold War-era nuclear treaty and must be called out on the breach, Britain's Chief of the Defence Staff has said.
It comes as NATO foreign ministers meeting in Brussels said they "strongly support the finding of the United States that Russia is in material breach of its obligations" under the 1987 Intermediate-range Nuclear Forces (INF) Treaty.
The Treaty 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.
The United States has threatened to withdraw from the pact unless Moscow complies with it.
Giving evidence to the Commons Defence Committee on Tuesday, General Sir Nick Carter was asked by Chairman Julian Lewis if he was convinced that Russia has broken the treaty to a significant degree.
Gen Carter said: "My view is that Russia is in breach of the treaty with the deployment of some of its systems which break the 500 to 5,000-kilometre range.
"And I am in no doubt that we need to call them out on that breach."
Pressed on whether we should withdraw from the agreement if Russia is not persuaded to remove the systems, Gen Carter said that is one course of action.
"But we also need to work out what measures we take to try and get them to obey with the rules that we laid and prescribed," he added.
The US government claims Russia's new SSC8 missile system contravenes the Cold War-era treaty, which bans all land-based cruise missiles with a range between 500 and 5,500 kilometres (310 to 3,410 miles).
In the wake of the decision, US Secretary of State Mike Pompeo said the United States would suspend its treaty obligations in 60 days over the alleged violations.
He added that "we either bury our head in the sand or we take common sense action" over Russia's contravention of the agreement.
The NATO foreign ministers have called on Russia "to return urgently to full and verifiable compliance. It is now up to Russia to preserve the INF Treaty".
US President Donald Trump has previously threatened to pull out of the bilateral pact.