"Great to be back from Vietnam, an amazing place," tweeted the president, who returned home late Thursday.

"We had very substantive negotiations with Kim Jong Un - we know what they want and they know what we must have," he wrote.

"Relationship very good, let's see what happens!" he added -- repeating a phrase he has often turned to when it comes to North Korea.

Eight months after their first summit in Singapore, the high-stakes second meeting between the two leaders broke up in abruptly Thursday without even a joint statement.

Each sought to blame the other's intransigence for the deadlock, with Trump insisting Pyongyang wanted the lifting of all sanctions imposed over its banned weapons programs, something US officials were unwilling to do.

North Korea's foreign minister however said Pyongyang had only wanted some of the measures eased, and that its proposal to close "all the nuclear production facilities" at its Yongbyon complex was its best and final offer.

Despite the apparent stalemate, the North's official KCNA news agency described the Hanoi meeting as "successful" and said Kim had promised Trump another encounter.