US President Donald Trump voiced confidence Saturday that Kim Jong Un would not "break his promise," following what if confirmed would be North Korea's first short-range missile launch for more than a year.
"Anything in this very interesting world is possible," Trump tweeted, after Seoul said Pyongyang had launched several unidentified projectiles into the sea.
"But I believe that Kim Jong Un fully realizes the great economic potential of North Korea, & will do nothing to interfere or end it," he added.
"He also knows that I am with him & does not want to break his promise to me. Deal will happen!"
Since their historic summit meeting in Singapore in 2018, Trump has said Kim remains committed to the "complete denuclearization" of the Korean peninsula.
He has insisted the two leaders remain close even after their follow-up meeting in Hanoi collapsed in February, and that Kim would maintain his moratorium on long-range missile and nuclear tests.
But with negotiations lagging, the North appears to be testing the US side.
The latest launch followed last month's test-firing of very-short-range tactical weapons, and it came days after a senior North Korean diplomat chastised US Secretary of State Mike Pompeo for making "foolish and dangerous" comments in nuclear talks with the North.
Analysts said Pyongyang appears intent on raising pressure on Washington as those talks remain deadlocked.
The two sides have been clashing over the North's demand for substantive economic sanctions relief and the US's insistence that the North make concrete concessions toward eliminating its atomic arsenal.
North Korea analyst Ankit Panda stressed that Saturday's launch "does not violate Kim Jong Un's self-imposed missile-testing moratorium," which "only applied to intercontinental-range ballistic missiles."
But a statement from South Korea's presidential Blue House said it was "greatly concerned," calling it a violation of a military agreement signed by both Koreas last year.
North Korea "fired a number of short-range projectiles" from Hodo peninsula near the east coast town of Wonsan starting at 9:06 am (0006 GMT), the South's Joint Chiefs of Staff said in a statement.
The projectiles traveled northeast from 70 to 200 kilometers (45 to 125 miles) towards the East Sea, also known as the Sea of Japan, the JCS added.
In an earlier statement, it had said Pyongyang launched an unidentified short-range missile.
The last North Korean missile launch was in November 2017.
The latest firing comes just a day after South Korean Foreign Minister Kang Kyung-wha said Pyongyang should show "visible, concrete and substantial" denuclearization action if it wants sanctions relief -- the issue at the center of the Hanoi debacle.
Earlier this week, North Korean Vice Foreign Minister Choe Son Hui warned Washington of an "unwanted outcome" if it did not adjust its stance on economic sanctions.
Hodo Peninsula, where Saturday's firing took place, has been used since the 1960s for "live-fire testing, training exercises for artillery and coastal defense cruise missiles," according to the respected 38 North website.
In recent years, Hodo has been "increasingly used for ballistic missile and long-range artillery rocket testing," it added.
Since the collapse of the Hanoi summit, South Korean president Moon Jae-in -- who brokered the first meeting between the mercurial US and North Korean leaders -- has tried to salvage diplomacy, but Pyongyang has remained largely unresponsive.
Last week, on the anniversary of the Panmunjom summit between Moon and Kim, Pyongyang's state media KCNA said Washington and Seoul "keep pushing the situation of the Korean peninsula and the region to an undesirable phase", criticizing their joint military exercises.
Saturday's launch came days before US special representative Stephen Biegun is to visit Japan and South Korea.
Washington had said Biegun would discuss "efforts to advance the final, fully verified denuclearization of North Korea" with officials in Seoul and Tokyo.
Seoul's nuclear envoy Lee Do-hoon spoke to Biegun on Saturday to discuss Pyongyang's latest launch, the South's foreign ministry said.
"Chairman Kim has decided to remind the world -- and specifically the United States -- that his weapons capabilities are growing by the day," said Harry J Kazianis, Director of Korean Studies at the Center for the National Interest.
"My fear is that we are at the beginning stages of a slide back to the days of nuclear war threats and personal insults, a dangerous cycle of spiking tensions that must be avoided at all costs."