"I urge you to extend your hands to the darkest places," Yoo said at the International Dialogue on North Korean Human Rights co-hosted by the Washington-based National Endowment for Democracy and the Ministry of Unification.
"It is not injustice itself but our indifference that nurtures injustice. If there is injustice anywhere in this world, do not close your eyes or turn away, but take action," he added.
The model-turned-actor has been working to raise global awareness of North Korean human rights issues as a promotional ambassador for the Ministry of Unification since last month.
In an opening address, Minister Kim Yung-ho also said, "Some 34,000 North Korean defectors who have settled in South Korea vividly describe the rogue country's human rights violations."
Yoo rose to stardom with villain roles in hit movies like "Attack the Gas Station" (1999) and "Oldboy" (2003). His recent work also includes Disney+' eight-episode series, "Vigilante" released in November last year. He has also directed several short films recently.
