The ultimatum from Berlin comes as Ukraine said Russia was still carrying out attacks along the front line, despite a ceasefire proposal agreed on the weekend among Kyiv's allies for a 30-day ceasefire to start Monday. The Kremlin said such an ultimatum "is unacceptable for Russia."

The chief of staff to Germany's new chancellor, Thorsten Frei, has called on Europe to step "out of our comfort zone" and impose tougher sanctions on Russia, such as banning gas and uranium imports and tapping into frozen Russian state assets.

The European Union is considering cutting more than 20 banks from SWIFT, the international payments system, as well as lowering a price cap on Russian oil and banning the Nord Stream gas pipelines as part of a new sanctions package that aims to increase pressure on Moscow to end its war against Ukraine.