"Massive" sanctions European leaders threatened to impose on Russia if Vladimir Putin does not agree to a ceasefire in Ukraine face formidable political obstacles and would need U.S. support to succeed,

"We are waiting for (Russian President Vladimir) Putin's agreement and we agree that if there is no real progress this week, we want to work together at European level for a significant tightening of sanctions," Merz said at a news conference with his Greek counterpart.

Russia’s economy is under growing strain as its invasion of Ukraine drags on and Western sanctions are undermining President Vladimir Putin’s ability to sustain his war, a leading European economist said after briefing finance ministers on Tuesday.