Russia started the conflict in Ukraine and can end it "straight away”, UK Prime minister Sir Keir Starmer has said, Azernews reports referring to BBC.

It comes after Russian President Vladimir Putin suggested Moscow would regard Western missiles being fired into Russia as a serious escalation of the war. Putin told Russian state television that this would “mean nothing other than the direct participation of Nato countries - the US and European countries - in the war in Ukraine."

Sir Keir is in Washington for talks with US President Joe Biden on Friday, as allies of Kyiv discuss giving Ukraine permission to fire their missiles at targets inside Russia. "It is their direct participation," he said. "And, of course, this substantially changes the very essence, the nature of the conflict.”

He added: “If that is the case, we will take corresponding decisions based on the threats that will be created to us.” Asked for his response to the remarks on his flight to Washington, the prime minister struck a robust tone repeatedly stating that Russia had started the war.

“Russia started this conflict. Russia illegally invaded Ukraine. Russia can end this conflict straight away,” he said.

He later added: “To reiterate, it was Russia who started this in the first place. They caused the conflict, they’re the ones who are acting unlawfully.”

The prime minister and Foreign Secretary David Lammy are on a blitz of international diplomacy, as Ukraine’s allies discuss how to respond to Iran stepping up its weapons support for Russia.