The US and Russian presidents have tentatively agreed to meet in a last-ditch diplomatic effort to stave off Moscow’s invasion of Ukraine as heavy shelling continued Monday in a conflict in eastern Ukraine that is feared will spark the Russian offensive.

French President Emmanuel Macron sought to broker a possible meeting between U.S. President Joe Biden and Russian President Vladimir Putin in a series of phone calls that dragged into the night. Macron’s office said both leaders had “accepted the principle of such a summit,” to be followed by a broader summit meeting also involving other “relevant stakeholders to discuss security and strategic stability in Europe.”