According to senior sources, the German Chancellor and French President “scrambled on to their plane” because of growing fears that Ukraine’s government is on the brink of collapse and the conflict is “on the edge of something palpably worse”.
“The sense is that the situation is radically deteriorating, both militarily and economically. Everyone is alarmed at intelligence showing the sheer extent of Russian troop involvement and the arming of rebels,” said a senior European diplomat.
Chancellor Merkel has taken the lead for the West, with British and American consent, because she has the best contacts with both Vladimir Putin, the Russian President and Petro Poroshenko, Ukraine’s besieged leader.
Mr Poroshenko has issued a desperate appeal for arms to fight what his government calls a war of “Russian aggression”.
She has denied reports that the West and Ukraine are ready to trade territory with Russian backed separatists in order to buy peace and has briefed diplomats over her pessimism that President Putin can be restrained.
"I will never deal with territorial questions over another country,” she said en route to Moscow.
Mrs Merkel will report back to EU leaders at a Brussels summit on Thursday and is expected, unless there is a new peace plan, to propose new economic sanctions against Russia.
Mr Putin is demanding the creation of new territory controlled by separatists on the model of so called “frozen conflict zones” such as Abkhazia or Transnistria, breakaway provinces of Georgia and Moldova that are under Russian military protection.
Russia is also demanding that the United Nations send peacekeepers to police a demilitarised buffer zone between West and East Ukraine, proposals that would tear up an agreement signed in Minsk last September.
“There has been no EU agreement on peacekeepers of any description as this poses the danger of a de facto partition of Ukraine,” said a diplomat.
Ahead of meeting with Joe Biden, the US vice-president, Donald Tusk, the Polish president of the European Council, stressed the importance of Ukraine's “territorial integrity”.
"The situation in Ukraine is getting worse every day," he said.
"We cannot accept any form of aggression, especially the aggression of one state against another. We cannot compromise on Ukraine's independence, sovereignty and territorial integrity. The EU remains fully committed to continuing our support for the Ukrainians."
Mr Biden, who will holding talks with Mrs Merkel i Munich at the weekend, warned "Ukraine is fighting for its very survival right now".
"Russia is escalating the conflict by sending mercenaries and tanks, special operation soldiers. President Putin continues to call for new peace plans as his soldiers roll through the countryside. He absolutely ignores every agreement that his country has signed in the past and recently, including in Minsk," he said.
"This is a moment when the US and Europe must stand together, must stand firm. Russia cannot be allowed to redraw the map of Europe because that is exactly what they are doing."