BRUSSELS (AFP, Reuters) - The United States and Europe must stand together over Ukraine as it battles for survival in the face of escalating Russian military involvement, Vice-President Joe Biden said during a visit to Brussels on Friday.

"We, the US and Europe as a whole, have to stand with Ukraine at this moment," he said, amid reports of transatlantic divisions over whether to send weapons to support the Western-backed Kiev government.

Biden also criticised Russian President Vladimir Putin, who is to meet the leaders of France and Germany in Moscow later Friday, of riding roughshod over peace efforts.

"Ukraine is fighting for their very survival right now," Biden told reporters alongside EU president Donald Tusk.

"Russia contines to escalate the conflict by sending mercenaries and tanks and, as we euphamistically say in the United States, little green men, without patches, very sophisticated special operations soldiers.

"President Putin continues to call for new peace plans as his troops roll through the Ukrainian countryside, and he abslutely ignores every agreemnent his country has signed in the past."

Biden made no mention of possible US arms supplies to Ukraine to fight separatists in the east of the country, which some European leaders fear would merely escalate the conflict.