Ukrainian President Petro Poroshenko, right, and European Council President Donald Tusk visit the memorial for Maidan activists who were killed during anti-government protests in 2014, dubbed the 'Heroes of the Heavenly Hundred', not far from the Independence Square in Kiev, Ukraine, Tuesday, Feb. 19, 2019. (Mikhail Palinchak, Presidential Press Service Pool Photo via AP)

A handout photo taken and released by the Ukrainian Presidential press service shows Ukrainian President Petro Poroshenko (R) and European Council Donald president Tusk (L) laying flowers at the Maidan activists memorial dubbed the "Heroes of the Heavenly Hundred", who were killed during anti-government protests in 2014, not far from the Independence Square in Kiev on February 19, 2019. (Photo by Mikhail Palinchak / UKRAINIAN PRESIDENTIAL PRESS SERVICE / AFP) / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO /Ukrainian Presidential press service" - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS

A handout photo taken and released by the Ukrainian Presidential press service shows Ukrainian President Petro Poroshenko (R) and European Council Donald president Tusk (L) laying flowers at the Maidan activists memorial dubbed the "Heroes of the Heavenly Hundred", who were killed during anti-government protests in 2014, not far from the Independence Square in Kiev on February 19, 2019. (Photo by Mikhail Palinchak / UKRAINIAN PRESIDENTIAL PRESS SERVICE / AFP) / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO /Ukrainian Presidential press service" - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS

A handout photo taken and released by the Ukrainian Presidential press service shows Ukrainian President Petro Poroshenko (R) and European Council Donald president Tusk (L) visiting the Maidan activists memorial dubbed the "Heroes of the Heavenly Hundred", who were killed during anti-government protests in 2014, not far from the Independence Square in Kiev on February 19, 2019. (Photo by Mikhail Palinchak / UKRAINIAN PRESIDENTIAL PRESS SERVICE / AFP) / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO /Ukrainian Presidential press service" - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS

Ukrainian President Petro Poroshenko, right, and European Council President Donald Tusk during a meeting in Kiev, Ukraine, Monday Feb. 18, 2019. (Mykhailo Markiv, Presidential Press Service Pool Photo via AP)

Ukrainian President Petro Poroshenko, right, and European Council President Donald Tusk greet each other during a meeting in Kiev, Ukraine, Monday Feb. 18, 2019. (Mykhailo Markiv, Presidential Press Service Pool Photo via AP)