As the U.S. and Russia push ahead – so far without Ukraine at the table – on talks to end the war, political and military leaders in Europe are fleshing out details of a plan for European forces to help ensure Moscow does not attack again.

The Kremlin said on Thursday that any plan to send European troops to Ukraine as part of a potential peacekeeping mission would be unacceptable for Russia and that it was monitoring such proposals with concern.

Moscow’s forces are three miles from Dnipropetrovsk, a province they have never invaded. If they cross in, the advance would be a morale blow to Ukraine and complicate any territorial negotiations.

French President Emmanuel Macron has called leaders from key European Union nations and the United Kingdom for an emergency meeting Monday.