US President Joe Biden and Russian President Vladimir Putin have agreed in principle to a summit over Ukraine, the French leader said on Monday, offering a possible path out of one of the most dangerous European crises in decades.

Financial markets edged higher on the glimmer of hope for a diplomatic solution even as satellite imagery appeared to show Russian deployments closer to Ukraine's border, while sounds of fighting were heard on Monday in the east, where Ukrainian government forces are fighting pro-Russian separatists.

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

"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 the office of Ukrainian President Volodymyr Zelenskiy were not immediately returned early on Monday.

Few details of the proposed summit, announced after a volley of phone calls between Macron, Biden, Putin, Zelenskiy, and British Prime Minister Boris Johnson, are clear.

Macron's office and the White House said the substance of the plan would be worked out by the U.S. Secretary of State Antony Blinken and Russian Foreign Minister Sergei Lavrov during their meeting planned for Feb. 24.

Moscow says 'no concrete plans' for Putin-Biden summit

The Kremlin said there are “no concrete plans” for a summit between U.S. President Joe Biden and Russian President Vladimir Putin, throwing into question the fate of a French proposal that seemed to offer fresh hope for averting an alleged Russian plan to attack Ukraine.

U.S. officials said the meeting, proposed by French President Emmanuel Macron, would occur only if Russia doesn’t invade Ukraine. The discussion would focus on security and strategic stability in Europe, followed by a second summit with relevant stakeholders, the French presidential office said in a statement.