The talks took place in the warring capitals of Moscow and Kyiv, from Washington and Riyadh, Saudi Arabia, to countries across Europe.

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."