US President Barack Obama speaking on Monday in Seoul talked about his vision of "a world without nuclear weapons," making direct appeals to North Korea and Iran, CNN reported.
According to the Los Angeles Times, he urged the two nations to "have the courage" to abandon their nuclear weapons programs or face greater isolation and economic distress.
Obama is in South Korea attending a nuclear terrorism summit where he will meet his Russian and Chinese counterparts Monday, the BBC reported.
Speaking to students at Hankuk University, Obama said the US was committed to reducing its nuclear arms stockpile and that the US was in a unique position to seek change but that a "serious sustained global effort" was necessary.
More from GlobalPost: Obama asks China to help rein in North Korea
The meeting is being attended by representatives from some 50 countries.
Obama's trip comes at a time of tense relations with Pyongyang. North Korea announced it plans to launch a long-range missile in the next three weeks which it says will put a satellite in orbit.
North Korea says the launch is scheduled in mid-April, to coincide with the 100th anniversary of the birth of the country late Great Leader Kim Il-sung.
Such an act would violate UN. Security Council Resolution 1874 and goes against a deal North Korea made with Washington earlier this month that it would not carry out nuclear or missile tests in return for food aid.