US President Joe Biden and Russian President Vladimir Putin shake hands during a meeting. File photo

US President Joe Biden and Russian President Vladimir Putin have agreed to a summit — to be held only if Moscow does not invade Ukraine, France announced on Monday.

Following a frantic new round of diplomacy to avert an all-out war the French leader said, offering is a possible path out of one of the most dangerous European crises in decades.

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The office of French President Emmanuel Macron said in a statement he had pitched to both leaders a summit on "security and strategic stability in Europe." The White House said in a statement that Biden had accepted the meeting "in principle" but only "if an invasion hasn't happened."

French President Emmanuel Macron gestures to the media during a meeting. File photo

Both leaders have said yes in principle to the summit, proposed by French President Emmanuel Macron, his office said, with the White House confirming Biden's willingness, though it was notably cautious.

A senior administration official told AFP: "Timing to be determined. Format to be determined so it's all completely notional."

The Elysee added that the summit will be expanded to "relevant stakeholders" and that preparations would start between Russia and the United States on Thursday.

The Ukrainian Territorial Defence Forces take part in a military drill outside Kyiv on Sunday. AFP

"We are always ready for diplomacy," White House Press Secretary Jen Psaki said. "We are also ready to impose swift and severe consequences should Russia instead choose war."

Messages seeking comment from the Kremlin and from the office of Ukrainian President Volodymyr Zelenskiy were not immediately returned early on Monday.

Many details about the proposed summit — which was announced after a volley of phone calls between Macron, Biden, Putin, Zelenskiy, and British Prime Minister Boris Johnson — are not clear.

Macron's office and the White House said the substance of the summit would be worked out by US Secretary of State Antony Blinken and Russian Foreign Minister Sergei Lavrov during their meeting planned for Feb. 24. What role Ukraine would play in the summit, if any, was also uncertain.