Former United Nations Secretary-General Ban Ki-moon speaks during the World Leaders Session at the Jeju Forum in Jeju Island, Thursday. Korea Times photo by Shim Hyun-chul SEOGWIPO, Jeju Island — Former United Nations Secretary-General Ban Ki-moon on Thursday criticized the United States for withdrawing from international organizations, warning that no country can survive without cooperating with the rest of the world.Speaking at the World Leaders Session, a key event of the annual Jeju Forum for Peace and Prosperity, Ban said he was "angry" over U.S. President Donald Trump's decision to pull out of dozens of international institutions."I am very angry that President Donald Trump has decided to withdraw from 31 U.N. organizations and 35 international organizations like WHO, UNESCO and UNFCCC," he said.Expressing concern over the weakening role of the U.N. and other international institutions, Ban appealed for Washington to reverse its course."I really appeal to the U.S. — please return. You are the leader," he said. "Not a single country in this world can live alone without working together with members of the international community."His remarks came after Trump in January signed a presidential memorandum directing the U.S. to withdraw from more than 60 international organizations, including 31 U.N. entities. The Trump administration argued that many of the organizations are ineffective and pursue agendas that run counter to U.S. interests.Panelists attend the World Leaders Session of the Jeju Forum at a hotel on Jeju Island, Thursday. From left are Gareth Evans, former Australian foreign minister; former United Nations Secretary-General Ban Ki-moon; Susilo Bambang Yudhoyono, former president of Indonesia; Yukio Hatoyama, former prime minister of Japan; Gombojav Zandanshatar, former prime minister of Mongolia; and Philipp Rosler, former vice chancellor of Germany. Korea Times photo by Shim Hyun-chulThe former U.N. chief also urged major powers to resume dialogue as geopolitical divisions deepen."There's growing rivalry among major powers like the United States, European Union, China and Russia. They are not talking with each other as much as they did during my time at the U.N. It's very worrisome," Ban said."Even the relationship between the U.S., E.U. and NATO is totally different from just a few months ago. I sincerely hope that the leaders of major powers can really work together, hand-in-hand."The session brought together former heads of state to discuss ways to strengthen multilateral cooperation in a time of growing geopolitical tensions.Participants included Ban; Susilo Bambang Yudhoyono, former president of Indonesia; Yukio Hatoyama, former prime minister of Japan; Gombojav Zandanshatar, former prime minister of Mongolia; and Philipp Rosler, former vice chancellor of Germany. Foreign Minister Cho Hyun, front row center, former United Nations Secretary-General Ban Ki-moon, front row fourth from left, and Jeju Special Self-Governing Province Governor Oh Young-hun, front row sixth from left, and other dignitaries pose during the opening ceremony of the Jeju Forum for Peace and Prosperity at a hotel on Jeju Island, Thursday. Korea Times photo by Shim Hyun-chul In a video message during the Jeju Forum's opening ceremony earlier in the day, President Lee Jae Myung said Korea would continue to promote international cooperation for peace and prosperity, pledging to fulfill its role as a responsible global actor."The challenges confronting the world today, including artificial intelligence, trade and climate change, cannot be solved by one or two countries acting alone," Lee said.He added that countries capable of addressing such challenges should build flexible networks of cooperation to help fill gaps in the existing international order.In a congratulatory video message, incumbent U.N. Secretary-General Antonio Guterres also underscored the importance of multilateralism."Multilateralism — the very idea that we can solve rural problems together — is under threat. To my mind, reinventing cooperation ultimately means renewing our commitment to common values and to the Charter of the United Nations," he said.The three-day Jeju Forum, held from Wednesday to Friday under the theme "Reinventing Cooperation in a Fragmented World," features about 70 sessions involving current and former government officials, diplomats, scholars and policy experts discussing global peace, security and sustainable development.