US President Donald Trump voiced confidence on Saturday that North Korea's Kim Jong Un would not “break his promise,” after South Korea said Pyongyang had launched several unidentified projectiles into the sea.

“Anything in this very interesting world is possible, but I believe that Kim Jong Un fully realises the great economic potential of North Korea, & will do nothing to interfere or end it,” Trump tweeted.

“He also knows that I am with him & does not want to break his promise to me. Deal will happen!” added the US president, in response to what could be Pyongyang's first short-range missile launch for more than a year.

Trump's statement came after North Korea fired several “unidentified short-range projectiles” into the sea off its east coast on Saturday, prompting South Korea to call on its communist neighbour to “stop acts that escalate military tension on the Korean Peninsula.”

A second summit between Kim and Trump in Hanoi in February failed to produce a deal to end Pyongyang's nuclear programme in return for sanctions relief.

'Several projectiles' fired

North Korea fired several unidentified short-range projectiles into the sea off its eastern coast on Saturday, the South Korean Joint Chiefs of Staff said, a likely sign of Pyongyang's growing frustration at stalled diplomatic talks with Washington meant to provide coveted sanctions relief in return for nuclear disarmament.

South Korea's military has bolstered its surveillance in case there are additional weapons launches, and South Korean and US authorities are analysing the details.

If it's confirmed that the North fired banned ballistic missiles, it would be the first such launch since the North's November 2017 test of an intercontinental ballistic missile. That year saw a string of increasingly powerful weapons tests from the North and a belligerent response from President Donald Trump that had many in the region fearing war.

The South initially reported on Saturday that a single missile was fired, but later issued a statement that said “several projectiles” had been launched and that they flew up to 200 kilometres before splashing into the sea toward the northeast.

Experts say the North may increase these sorts of low-level provocations to apply pressure on the United States to agree to reduce crushing international sanctions.