North Korea fired two short-range missiles into the sea on Thursday, South Korea's Joint Chiefs of Staff said, after warnings from Pyongyang over military exercises between Washington and Seoul next month.
The North has warned the war games could affect the planned resumption of denuclearisation talks between Washington and Pyongyang.
The North fired the two missiles just after dawn, an official at South Korea's Joint Chiefs of Staff said, and they flew a distance of around 430 kilometres (260 miles) before falling into the East Sea, also known as the Sea of Japan.
"It's not clear whether Kim Jong Un oversaw the launch on site", he said, referring to the North's leader.
A joint analysis of the weapons was underway with Washington, the official told AFP.
Tokyo said the launches did not reach Japanese waters, with Japan's defence minister calling Pyongyang's move "extremely regrettable".
"We have confirmed so far that they did not reach our country's territory or exclusive economic zone," Defence Minister Takeshi Iwaya told reporters.
Pyongyang last fired short-range missiles on May 9, which US President Donald Trump called "very standard stuff" that, he said, had not affected his relationship with the North's leader Kim Jong Un.
Kim and Trump agreed to a resumption of dialogue at an impromptu June 30 meeting they held in the Demilitarized Zone that divides the two Koreas.
Following that meeting, US Secretary of State Mike Pompeo said working-level talks would probably start in mid-July.
But last week, North Korea issued a warning over the military drills, which have been held for years and were scaled down to ease tensions with the nuclear-armed state.
The North condemned the exercises as "blatant pressure" and a "violation of the spirit" of the joint statement Trump and Kim signed at their first summit in Singapore last year.
The North even hinted it could reconsider its moratorium on nuclear testing because of the drills, although the US State Department had remained upbeat over commitments made by Kim and Trump during the DMZ encounter and at a February summit in Vietnam.
"The action should be considered part of Pyongyang's protest against the upcoming US-South Korea military drill next month," said Cheong Seong-chang, an analyst at the Sejong Institute.
But other analysts said opposition to the drills was merely a pretext for Pyongyang to pursue its weapons ambitions.
"I think today's launches are part of a larger plan for North Korea's advanced missile programme, rather than its protest against the upcoming military drill," said Hong Min, a senior researcher at the South's state-run Korea Institute for National Unification.
"The North has declared in the past it would modernise and improve its defence system.... The launches today are part of that development plan and I think the North had already planned the launches in advance", he added.
Adam Mount, of the Federation of American Scientists, said the latest launch was a clear indication that "North Korea's nuclear and missile arsenals are now routinely being improved, displayed, and tested."
"The current bargain is: don't test nuclear warheads or long range missiles and the United States won't object or seriously try to stop it," Mount tweeted.
At their first summit in Singapore in June 2018 Trump and Kim adopted a vaguely worded statement on "complete denuclearisation of the Korean peninsula" and agreed to "establish new US-DPRK relations".
But the failure to reach an agreement over relief from US sanctions, and what the North was willing to give in return, led to the collapse of the leaders' second summit in Hanoi.
Tensions rose in May, during the standstill in negotiations between Trump and Kim, when North Korea fired short-range missiles for the first time since November 2017.
"I don't consider that a breach of trust at all. And, you know, at some point I may. But at this point no," Trump said in an interview with Politico at the time.
Asked on Tuesday whether any meetings were scheduled with the North, Trump said: "No, we just have a very good relationship. And probably they would like to meet and we'll see what happens."
"There was a little correspondence recently, very positive correspondence with North Korea."
He said there had been "no nuclear testing, there's no missile testing, there's no nothing."
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