June 5 (UPI) -- Ukrainian President Volodymyr Zelensky challenged Russian President Vladimir Putin to meet him face-to-face to try to bring the four-year-long war between their two countries to an end. In an open letter to Putin late Thursday, Zelensky said Ukraine wanted to end the conflict through "direct engagement," adding that it was incumbent on the sides to act, rather than waiting for Washington to take the lead -- but other agreed participants such as the United States and European