North Korean leader Kim Jong Un left Vietnam on Saturday by heavily armed train after his second summit with US President Donald Trump ended early and without success.
Kim's journey from Hanoi to Pyongyang will take two days and will cover two thousand eight hundred miles of track.
But the communist leader is returning empty-handed to his isolated country.
His offer to dismantle the Yongbyon nuclear facility in exchange for a lifting of all sanctions was rejected by the US.
Trump said the two days of talks in Hanoi made good progress but it was important not to rush into a bad deal. He said he had walked away because of unacceptable North Korean demands.
"Basically, they wanted the sanctions lifted in their entirety, and we couldn't do that," he said.
One US official, who spoke on condition of anonymity with Reuters news agency, said North Korea was unwilling to completely freeze its weapons programmes.
"So to give many, many billions of dollars in sanctions relief would in effect put us in a position of subsidising the ongoing development of weapons of mass destruction," the official said.
Both the United States and North Korea have said they intend to continue talks, but have not said when a next round might take place.
In a move that could encourage more talks, U.S. officials said on Friday the United States and South Korea are expected to announce that they will not carry out large-scale spring joint military exercises, replacing them with smaller-scale drills.
The allies suspended a number of military drills before and after the first Trump-Kim summit last year to encourage talks with North Korea, which denounced the exercises as training for invasion.
Trump has repeatedly complained about the expense of the exercises and did so again after the Hanoi summit.
Trump and Kim first met in Singapore last June and agreed to establish new relations and peace in exchange for a North Korean pledge to work toward complete denuclearisation of the Korean peninsula.
North Korean Foreign Minister Ri Yong Ho said after Trump left Hanoi that North Korea had sought only a partial lifting of sanctions "related to people's livelihoods and unrelated to military sanctions."
He said it offered a realistic proposal involving the dismantling of all of its main nuclear site at Yongbyon, including plutonium and uranium facilities, by engineers from both countries.
While North Korea's official media said Kim and Trump had decided to continue talks, its Vice Foreign Minister Choe Son Hui has struck a more negative tone, telling reporters Kim "might lose his willingness to pursue a deal".
"It occurs to us that there may not be a need to continue," she said, adding that North Korea had taken "many steps" to try to reach a deal.
But North Korea's state news agency was conciliatory, quoting Kim as expressing gratitude to Trump for putting in efforts to get results and calling their exchanges constructive.
It made no mention of the breakdown of the summit.
The United Nations and the United States ratcheted up sanctions on North Korea when it conducted repeated nuclear and ballistic missile tests in 2017.
Washington has demanded North Korea's complete, verifiable and irreversible denuclearisation before sanctions can be lifted, a position Pyongyang has denounced as "gangster like."