European Council President Donald Tusk visited Nagasaki and Hiroshima on Wednesday to pay his respects to the victims of the 1945 U.S. atomic bombings of the cities, ahead of a Group of 20 summit to be held in Osaka later this week.

In a first official visit by an EU leader to the two cities, Tusk toured memorial museums on the wartime atomic bombings and held talks with Nagasaki Mayor Tomihisa Taue and Hiroshima Mayor Kazumi Matsui, laying flowers at the cenotaphs.

"It is you, the leaders of world superpowers, who are responsible for the fact that the lesson of Nagasaki will not be in vain," Tusk said in his speech at the Peace Park in central Nagasaki after offering flowers.

In an effort to raise awareness of the devastation caused by the atomic bombings and promote nuclear abolition, Nagasaki and Hiroshima have asked leaders of the G20 countries and organizations participating in the two-day gathering from Friday to visit the cities in addition to Osaka.

"I will tell them what I heard from you today that you expect determination and courage in their actions for nonproliferation and disarmament, peace and mutual respect," Tusk said during his visit to Hiroshima, adding the leaders should come to the two cities.

In August last year, U.N. Secretary General Antonio Guterres attended an anniversary ceremony commemorating the atomic bombing of Nagasaki, becoming the first sitting chief of the international body to do so.

Pope Francis will visit Hiroshima and Nagasaki on Nov. 24 during his four-day stay, the first papal visit to Japan since John Paul II in February 1981, according to sources close to the matter.