US President Donald Trump said that "nobody's happy" after North Korea raised the pressure over the future of their deadlocked nuclear negotiations by launching two short-range missiles.
Trump's second summit with North Korean leader Kim Jong Un in Hanoi in February broke up without an agreement or even a joint statement as the two failed to reach a deal on what Pyongyang would be willing to give up in exchange for relief from sanctions imposed over its banned nuclear weapons and ballistic missile programmes.
Since then Kim has accused Washington of acting in "bad faith" and given it until the end of the year to change its approach.
In what South Korea President Moon Jae-in termed an "element of protest", the North "fired what appeared to be two short-range missiles" on Thursday, Seoul's Joint Chiefs of Staff (JCS) said in a statement.
They were launched from Kusong in North Pyongan province, it said, and flew eastwards for 270 and 420 kilometres (170 and 260 miles) across the North.
It was Pyongyang's second such move in less than a week, after having not launched a missile since November 2017, shortly before a rapid diplomatic thaw eased high tensions and paved the way for the historic first Kim-Trump summit in Singapore last June.
At a White House event, Trump said US authorities were looking "very seriously" at the launch of the "short-range missiles".
"Nobody's happy about it," he told reporters.
"We'll see what happens," he added. "I know they want to negotiate, they're talking about negotiating. But I don't think they are ready to negotiate."
Thursday's launches came hours after the US Special Representative on North Korea, Stephen Biegun, arrived in Seoul for talks with South Korean officials, in his first visit since the Hanoi summit.