The U.S. government announced the seizure of North Korean cargo ship allegedly used to sell coal in violation of global sanctions.
However, on Saturday, North Korea also launched at least one short-range ballistic missile, which analysts said could reach up to 500km.
Harry Kazianis of the Centre for the National Interest added that the North had "once again chosen a course of action today that can only worsen already growing tensions".
Kim emphasized the necessity of boosting defense capability "to carry out combat tasks and keep full combat posture to cope with any emergency as required by the prevailing situation", the Korean Central News Agency said.
South Korea's military said it had stepped up monitoring and security in case of another launch, and was working with the United States to get additional information on the missiles involved. "I believe they will keep escalating by using what appear to be short-range missiles, something that will not cause the USA to react right away".
North Korea has fired two suspected short-range missiles from the west of the country, according to reports.
As North Korea conducted another rocket launch after the discussions, Moon said, the government needs public consensus on the food aid issue.More news: The Newest Tariffs Will Hit Consumers Harder
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The Republic of Korea (ROK)'s Joint Chiefs of Staff said Thursday that two projectiles were launched at around 4:30 p.m. from Sino-ri in the DPRK's North Pyongan Province in an eastward direction.
Pompeo first changed his plans to have meetings on Iran after U.S. President Donald Trump on Wednesday imposed fresh sanctions on Iran over its nuclear program.
Trump and Kim took unprecedented steps previous year toward ending this decades-long hostility by becoming the first leaders of their respective countries to meet face-to-face during a June summit in Singapore.
"Kim Jong Un has given the United States until the end of the year to rethink its approach", he said.
Choi Hyun-soo, a spokesperson from ROK's defense ministry, said at a regular press briefing that the ministry was deeply anxious about the DPRK's projectile launches, which violate the spirit of the inter-Korean comprehensive military agreement. And President Donald Trump said North Korea may not be ready to negotiate, indicating that a negotiated de-escalation of the latest crisis may not be quick in coming.
The test of two short-range missiles on Thursday and the firing of a series of projectiles on Saturday were the first missile launches by the North since November 2017 when the North shot an intercontinental ballistic missile (ICBM).
"If its flight path and accuracy were marginal or inconsistent with known Iskander trajectories and performance, then I think some form of local development with external technical assistance is more likely", he said. The country is barred from ballistic missile launches under U.N. Security Council resolutions.
But the North appeared to have refrained from using weapons that directly threaten the United States, Moon said.