U.S. Secretary of State Mike Pompeo has held telephone talks with presidential candidates Volodymyr Zelensky and Petro Poroshenko and expressed willingness to work with the winner of the vote, Kurt Volker, the U.S. Special Representative for Ukraine Negotiations, has said.

"Secretary Pompeo called both candidates tonight to underscore support for Ukraine's sovereignty & territorial integrity," he wrote on Twitter.

In addition, according to Volker, Pompeo "reiterated our commitment to working with whomever the Ukrainian people choose to ensure the success of a secure, prosperous, democratic, & free Ukraine."