A senior US official said the Trump administration was aware of the reports of a possible North Korean missile launch and that it was "continuing to monitor the situation and consulting closely with our allies in the region".
Seoul's presidential Blue House said that it will closely consult the US intelligence over the missile launch and believe it was likely to be a test of a submarine-launched ballistic missile.
The latest provocation from Pyongyang comes a day after it announced that the two sides would hold their first working-level meeting in months.
"It is a warning to the US that North Korea will not make any concessions in the upcoming working-level talks so come to the negotiating table with 'new calculations' including sanctions relief," said Shin Beom-chul, a researcher at the Asan Institute for Policy Studies in Seoul. "It is a message that Pyongyang will keep making military provocations unless Washington makes more concessions in the negotiations."
Mr Trump and Mr Kim met in late June in the demilitarised zone, or DMZ, that divides the Korean peninsula, in a hastily arranged meeting designed to resurrect the denuclearisation negotiations that had collapsed several months earlier in Hanoi.
The meeting also marked the first time a sitting US president stepped over the border into North Korea.
Last week Mr Trump met Moon Jae-in, South Korea's president, at the UN General Assembly in New York, rekindling hopes that the nuclear talks would resume.
Seoul has been pushing for negotiations to restart and welcomed the plan to revive discussions. A presidential office spokesperson said South Korea was "looking forward to seeing the actual progress toward complete denuclearisation and permanent peace regime on the Korean peninsula at an early stage".
Talks have stalled since the Hanoi summit in February, which was the second face-to-face meeting between the leaders after the pair held a historic meeting in Singapore last year.
North Korea had said it was willing to restart talks with the US in September, but hours later began testing weapons, which was described by analysts as a negotiating tactic. Since May, Pyongyang has undertaken short-range missile and rocket tests, raising fears of a return to military provocation.
The North Korean announcement comes against a backdrop of increasing scepticism about Pyongyang's intentions.
"Pyongyang is signalling that the upcoming negotiations are not going to be easy. After boycotting working-level talks for months, the North Koreans do not plan to show up with concessions. They are demanding the US come to the table offering more than it did in Hanoi," said Leif-Eric Easley, a professor at Ewha Womans University in Seoul.
Analysts said the two sides would struggle to work out a road map towards denuclearisation amid a lack of mutual trust.
"There are much lower expectations for North Korea's denuclearisation now than last year as we are watching the same old movie again," said Lee Seong-hyon, a researcher at the Sejong Institute, a think-tank.
"At the end of the day, the US and North Korea will face mutually irreconcilable differences in their road map towards denuclearisation. They still have the same old problem, which is a lack of trust in each other. They still struggle to hammer out a road map, haggling over who makes a concession first."
Kim Jae-chun, a professor at Sogang University in Seoul and a former government adviser, said the two sides were too far apart to reach a deal.
"The US wants to define denuclearisation and specify the scope of it even if it gets implemented step by step, but North Korea still finds it burdensome to draw a big picture. The two sides have too big differences of opinion over denuclearisation to narrow the gap," he said.
John Bolton, Mr Trump's recently ousted national security adviser, said in a talk last month that he did not believe Pyongyang would willingly surrender its nuclear weapons.
Additional reporting by Primrose Riordan in Hong Kong
Written by: Demetri Sevastopulo in Washington, Robin Harding in Tokyo and Song Jung-a in Seoul
© Financial Times 2019