SEOUL/WASHINGTON (Reuters) - South Korean President Moon Jae-in on Tuesday said North Korea should swiftly return South Koreans and Americans detained in the reclusive nation and that Pyongyang had “a heavy responsibility” in the death of a U.S. university student.

FILE PHOTO: South Korean President Moon Jae-in delivers a speech during a ceremony marking Korean Memorial Day at the National Cemetery in Seoul, South Korea, June 6, 2017. REUTERS/Kim Hong-Ji/File Photo

Moon, who is scheduled to visit Washington next week for talks with U.S. President Donald Trump, also told CBS in an interview that he hoped to draw North Korea into negotiations on its nuclear program by the end of the year, while talks with the United States about military options could wait.

Dozens of North Korean missile launches and two nuclear bomb tests since the start of last year and Pyongyang’s vow to develop a nuclear-tipped missile capable of hitting the U.S. mainland have put North Korea at the forefront of global security concerns.

Moon’s remarks on CBS’s “This Morning” program came the day after the death of Otto Warmbier, the 22-year-old American student who had been held prisoner in North Korea for 17 months. Warmbier died at a Cincinnati hospital just days after North Korea released him from captivity in a coma.

Moon said that while “we cannot know for sure that North Korea killed Mr. Warmbier ... I believe it is quite clear that they have a heavy responsibility in the process that led to Mr. Warmbier’s death.

“I believe we must now have the perception that North Korea is an irrational regime,” said Moon, who was elected in May.

“Even today, there are many Korean nationals and American citizens who are detained in North Korea,” Moon said. “I also urge North Korea to return these people to their families.”

North Korea has detained two Korean-American academics and a missionary, a Canadian pastor and three South Korean nationals who were doing missionary work there. Japan says at least several dozen of its nationals are being held in the country.

Moon, who was elected on a plan to engage in talks with North Korea, said he agreed with Trump on being willing to participate in a dialogue with North Korea under certain conditions, given that sanctions and international pressure have not resolved the situation.

“First we must vie for a freeze of North Korea’s nuclear and missile programs,” Moon said. “And then, as a second phase, try to achieve the complete dismantlement of North Korea’s nuclear program. And I believe there are voices supporting such a step-by-step approach even within the United States.”

Signaling a major shift in U.S. policy, Trump said earlier this year that he was willing to talk to North Korean leader Kim Jong Un to try to stop Pyongyang’s nuclear program.

“He mentioned that it would be an honor to be able to meet Kim Jong Un,” Moon told CBS. “So I believe President Trump went much further than I did.”

CONFLICTING RHETORIC

Trump has delivered conflicting rhetoric on North Korea and its leader, whom he has called a “madman with nuclear weapons.” On Monday, he blamed the “brutality of the North Korean regime” for Warmbier’s death. Warmbier was arrested while visiting North Korea as a tourist and accused of trying to steal a propaganda slogan, according to North Korean media. Doctors caring for him last week described him as having extensive brain damage that left him in a state of “unresponsive wakefulness.”

North Korea said last month that it was its sovereign right to “ruthlessly punish” U.S. citizens it had detained for crimes against the state. Warmbier’s death has shocked many Americans, making any direct U.S. contact with North Korea politically risky any time soon.

A Japanese diplomat said Warmbier’s death showed that now was not the time to talk to North Korea and that allies must maintain unity in pressuring Pyongyang with sanctions.

“We must not show them a weakness or a gap in our united front that they would exploit for their own purposes,” said the diplomat, who requested anonymity.

North Korea will dominate Moon’s June 29-30 summit with Trump.

Pyongyang has continued to test-fire missiles since Moon took office, despite his pledges to engage in dialogue.

Asked about the possibility of pre-emptive strikes against Pyongyang, Moon told CBS the issue could be raised at the summit with Trump, but such discussions were more likely to come later.

“This is something we may be able to discuss at a later stage when the threat has become even more urgent,” he said, adding that the North Korea nuclear missile threat was a matter of life or death for the South Koreans who live next door.

He said that if Trump could resolve the North Korean nuclear issue and bring peace to the Korean Peninsula and overall greater security in northeastern Asia, it would probably be the U.S. president’s greatest diplomatic achievement.

(For a graphic on Americans detained by North Korea, click tmsnrt.rs/2r5xYpB)