It is a week of intense diplomacy following Trump’s upending of U.S. policy with his decision to hold direct talks with Russia, while excluding Ukraine, European allies from initial discussions.

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.

Russian President Vladimir Putin said on Monday that Russia was not opposed to Europe's involvement in Russia-U.S. peace talks aimed at settling the conflict in Ukraine, but noted that Brussels had long rejected any dialogue with Moscow.