'Confident' Zelensky wants no involvement in U.S. politics -Senator Murphy

The United States has been the most powerful backer of Ukraine in its standoff with Russia over Moscow's 2014 annexation of Crimea and support for separatist fighters in a simmering conflict in the eastern Donbass region.

But their relationship was tested after Trump froze nearly $400 million in security aid and pressed Ukrainian President Volodymyr Zelenskiy to investigate one of the Republican president's Democratic rivals, former vice president Joe Biden.