US President Donald Trump says Kim Jong-un has told him North Korea is ready to resume talks on its nuclear and missile program as soon as US-South Korea military exercises end.
North Korea fired what appeared to be two short-range missiles on Saturday, South Korea said, in a "show of force" against the military exercises.
More missile launches are highly probable as the North Korean military is conducting its own summer drills, South Korea's joint chiefs of staff said in a statement.
The launch came a few hours after Trump said he had received a "very beautiful letter" from Kim.
Trump tweeted on Saturday that Kim complained of the "ridiculous and expensive" exercises and would like to meet and start negotiations as soon as the joint drills were over.
North Korea has fired a series of missiles and rockets since Kim and Trump agreed at a June 30 meeting to revive stalled denuclearisation talks.
A US official said that at least one projectile was launched and that it appeared to be similar to previous short-range missiles fired by Pyongyang.
Two missiles flew about 400km at a height of around 48km, according to the South Korean military.
Trump played down the recent North Korean weapons launches when he spoke to reporters on Friday.
"I say it again: There have been no nuclear tests. The missile tests have all been short-range. No ballistic missile tests. No long-range missiles," he said.
North Korea's state media has yet to confirm the launch, but in a commentary on Saturday it blamed the South for "building up arms against dialogue".
"All the facts prove that the South Korean authorities are hell-bent on arms buildup against their dialogue partner," the state-run KCNA news agency said.
South Korea called for Pyongyang to stop such launches.
The launches on Saturday were apparently testing the capabilities of a new short-range missile Pyongyang is developing, South Korea's presidential office said.
"Because of concerns that North Korea's series of launches can raise military tensions on the Korean Peninsula, ministers called for North Korea to stop it," the Blue House said, citing a meeting of South Korea's top security officials.
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Kim has said the weapons tests were a response to US-South Korean drills being held this month.
They have kicked off largely computer-simulated exercises as an alternative to previous large-scale annual drills that were halted to expedite denuclearisation talks.
North Korea decries such exercises as a rehearsal for war aimed at toppling its leadership.
The projectiles were fired at dawn on Saturday from an area around the northeast city of Hamhung, South Korea's joint chiefs of staff said in a statement.