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.
Defense secretary James Mattis and Secretary of State Rex Tillerson are expected to raise Warmbier's death and the related issues the U.S. has with Pyongyang at their meeting with their Chinese counterparts in town for the annual diplomatic and security dialogue on Wednesday.
American concern is growing over North Korea's acceleration toward having a nuclear missile that can strike the US mainland. Later, he reached an accord with the Chinese leader, remaining hopeful while conceding that the Sino-North Korean relationship was more complicated than meets the eye.
The travel agency specializes in North Korea tours and is based in the central Chinese city of Xi'an.
U.S. Sen. John McCain says Americans who are "stupid" enough to still want to visit North Korea should be required to sign a waiver absolving the U.S. government of any blame if they're harmed while there.
His family has said that Warmbier lapsed into a coma in March 2016, shortly after he was sentenced to 15 years of hard labor in North Korea. Other travel companies say they're considering a similar restriction. Seen from one angle, China has declared its support for United Nations sanctions against Pyongyang aimed at crippling its nuclear weapons and missile development. But on Tuesday, Trump suggested that strategy had failed.
It is impossible to get reliable information about the welfare and treatment of foreigners detained in North Korea - Washington only learned of Otto Warmbier's condition in early June. South Korea, therefore, must try to bring Pyongyang back to the negotiation table, letting the regime know that giving up its nuclear program is not only the right path but the only path. President Moon had also sat down with "CBS This Morning" co-host Norah O'Donnell for an interview as well, which aired Tuesday morning, local time.
In Congress, Democrats and Republicans found rare bipartisan consensus in denouncing North Korea. No licenses would be issued for tourism.
Under existing law, all it would take is a designation by Tillerson - called a "geographic travel restriction" - to make all American passports invalid for travel to North Korea.
Chinese state-run newspaper the Global Times, published by the official People's Daily, said Chinese officials must be wary that Warmbier's death might push Washington to put greater pressure on Beijing.
Yun is a US special envoy.
Portman says the officials indicated they would relay his request to free University of Virginia student Otto Warmbier (WORM'-bir), who had been held almost a year at that point.