Library picture of Gavin Williamson with US Defence Secretary Jim Mattis (Picture: PA).
The Defence Secretary Gavin Williamson pointed the blame at Russia for endangering the Intermediate-Range Nuclear Forces (INF) Treaty - after US President Donald Trump said he would pull out of a landmark nuclear pact with Russia.
Donald Trump said Russia had "violated" the pact.
The INF was agreed by the US and Soviet Union in 1987, and called on the Kremlin to "get its house in order".
Russia has been accused of developing new missiles in contravention of the INF several times in recent years.
Mr Williamson accused Russia of breaking the agreement, saying Moscow had made a "mockery" of the INF.
"It is Russia that is in breach and it is Russia that needs to get its house in order."
"Our close and long-term ally, of course, is the United States and 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," he told the Financial Times.
The Defence Secretary is in the US while the Royal Navy aircraft carrier HMS Elizabeth visits New York.
"We, of course, want to see this treaty continue to stand but it does require two parties to be committed to it and at the moment you have one party that is ignoring it," Mr Williamson said.
Mr Trump did not detail any recent violations of the pact, although in 2017 White House national security officials said Russia had deployed a cruise missile in violation of the treaty.
The Kremlin was also accused of breaking the agreement by former US President Barack Obama's administration.
Russia has claimed that US missile defences violate the pact.