Russian President Vladimir Putin would "sooner or later" have to "come to the table" as he opened a virtual gathering to drum up support for Ukraine, British Prime Minister Keir Starmer said on Saturday.

"My feeling is that sooner or later, he's going to have to come to the table and engage in serious discussion," Starmer told about 25 fellow leaders who joined the virtual summit.

The talks hosted in a call set up by Downing Street aim to urge participating countries to sign up to a coalition willing to protect any eventual ceasefire in Ukraine.

Starmer told allies the meeting would focus on three points "strengthening Ukraine, being prepared to defend any deal ourselves through a coalition of the willing, and keeping that pressure on Russia at this crucial time."

He said Ukraine's President Volodymyr Zelensky had shown that Ukraine was the "party of peace because he has agreed to and committed to a 30-day unconditional ceasefire".

"Putin is the one trying to delay... if Putin is serious about peace, I think it's very simple, he has to stop his barbaric attacks on Ukraine and agree to a ceasefire, and the world is watching," he added.

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This comes after Reuters reported that Russia now views Britain as its primary enemy citing three Russian officials speaking on the condition of anonymity.

This title was reportedly earned after two British diplomats were expelled from the country over espionage charges, a ferocious statement from Russia's SVR calling Britain "a warmonger", and a threat from a top ally of Vladimir Putin to seize UK assets inside Russia.

The three Russian officials confirmed that Russia now views Britain as its "public enemy number 1," describing the UK as the main driving force behind the West's opposition to Russia, while another expressed his anger accusing London of "stoking chaos and war" in Ukraine, according to Reuters.

One official accused London of leading the efforts against Russia in Ukraine, describing the UK as "the locomotive" that pulls others along with it.

"London today, like on the eve of both World Wars of the last century, is acting as the main global 'warmonger'," Russia's Foreign Intelligence service said in a statement published on Monday, accusing the UK of trying to derail Trump's efforts to bring the Russo-Ukraine war to an end.