U.S. President Donald Trump said that "nobody is happy" at the launches, but appeared to hold the door open for more talks with the North. South Korea said the tests were worrisome and unhelpful and likely a protest against Trump refusing to ease economic sanctions at a failed summit with North Korean leader Kim Jong Un in February.

Washington has given no sign of willingness to budge on sanctions and the U.S. Justice Department announced on Thursday the seizure of a North Korean cargo vessel it said was involved in the illicit shipping of coal.

Pyongyang has effectively pulled back from engagement with Washington since the February meeting between Kim and Trump in Hanoi collapsed without agreement on U.S. demands for the dismantling of Pyongyang's nuclear program and Kim's demands for relief from punishing sanctions.

"The relationship continues. ... I know they want to negotiate, they're talking about negotiating. But I don't think they're ready to negotiate," Trump told reporters.

Acting U.S. Defense Secretary Patrick Shanahan said Washington would continue to focus on diplomatic efforts with North Korea.

"We're going to stick to our diplomacy and as you all know, we haven't changed our operations or our posture and we'll continue to generate the readiness we need in case diplomacy fails," he told reporters.

Trump has held up a freeze in missile testing since 2017 as a sign of progress in his talks with North Korea after exchanges of fiery rhetoric two years ago raised fears of war.

DPR Korea formally announced a freeze in intercontinental ballistic missile (ICBM) and nuclear bomb tests in April last year and Trump stressed that the missiles fired were not of a kind that could threaten the United States.

"We're looking at it very seriously right now. They were smaller missiles, they were short-range missiles," he said. "Nobody's happy about it but we're taking a good look and we'll see."

The Pentagon said the launches consisted of multiple ballistic missiles that flew in excess of 300 km (185 miles) and landed in the ocean.

The North's official KCNA news agency reported that Kim oversaw the army "strike drill," and said he noted that "genuine peace and security of the country are guaranteed only by the strong physical force capable of defending its sovereignty."

White House Chief of Staff Mick Mulvaney played down the tests, telling CBS News the "supposed provocation" was "very minor."

"These missiles, whatever they were, whatever you want to call them, they were very small. And not aimed at Japan, not aimed at Guam, they were aimed up the North Korean coast. So it was a very non-provocative provocation if there is such a thing."

He said the relationship between Kim and Trump remained good and he was confident there would be more talks with the North. "We want additional talks," he said.

Asked if the U.S. side wanted another summit, he said: "Eventually? Yeah, I think we do," while adding that at the last summit, the North Koreans "were not really willing to negotiate.'

"They gave us an offer - you know, a take-it-or-leave-it offer - five different times. And we couldn't take it, so we had to leave."

U.N. Secretary-General Antonio Guterres urged all parties to continue talks toward denuclearization, warning that Pyongyang's latest action "serves only to increase tensions."

On Saturday, Kim oversaw the test-firing of multiple rockets and a missile. That was DPR Korea's first test of a ballistic missile since an ICBM launch in November 2017 that it said was capable of delivering a warhead anywhere in the United States.

South Korea's Joint Chiefs of Staff said the two missiles fired on Thursday flew east from the northwestern area of Kusong and covered 420 km (260 miles) and 270 km (168 miles) and reached an altitude of about 50 km (30 miles) before falling into the sea.

South Korean President Moon Jae-in, who has strongly advocated engagement with North Korea, said that even if the missiles were short-range, they could still violate U.N. resolutions barring the North from developing ballistic missiles.

"North Korea seemed to be discontented it could not reach a deal in Hanoi," he told South Korean broadcaster KBS, while adding that he saw the tests as a sign that the North wanted to negotiate. He said he planned to push for a fourth inter-Korean summit with Kim.

U.S. Secretary of State Mike Pompeo met on Thursday with Japan's chief Cabinet secretary, Yoshihide Suga, who was expected to raise Japanese Prime Minister Shinzo Abe's hopes for a summit with Kim.

Trump and Pompeo have brushed aside Kim's demand for Washington to show more flexibility in talks by the end of the year.

REUTERS