North Korea fired five short- range missiles into the sea off its eastern coast in its latest protest against international pressure, barely an hour before officials from Seoul and Washington began discussions on new United Nations sanctions.
The two allies are fully committed to implementing the UN sanctions "with vigour and energy", said Ambassador Sung Kim, United States special representative for North Korea policy, after his meeting in Seoul yesterday with his South Korean counterpart Kim Hong Kyun and the US State Department's coordinator for sanctions policy Daniel Fried.
"Both countries are reaching out to others in the region and beyond to ensure everyone is implementing this important resolution fully," said Ambassador Kim, who will be travelling next to Vietnam and Cambodia for talks with officials on UN sanctions.
He called on Pyongyang to refrain from all provocative actions, including missile tests, which violate UN Security Council resolutions.
South Korean President Park Geun Hye, during a regular meeting in her Blue House office, urged officials to remain vigilant and be thoroughly prepared to cope with any form of provocation from the North.
South Korea's military raised its alert, while the Unification Ministry said the government is preparing for "all possibilities", including a fifth nuclear test by North Korea.
This came amid reports of continued activity at Pyongyang's nuclear experiment site, after North Korean leader Kim Jong Un declared last week that his country will soon conduct a nuclear warhead explosion test and test-fire ballistic rockets capable of carrying nuclear warheads.
He did not give a specific time frame, but Seoul believes that Pyongyang is technically ready and capable of conducting a fifth nuclear test "immediately", said Unification Ministry spokesman Jeong Joon Hee.
North Korea conducted its fourth nuclear test in January, followed by a rocket launch last month and two rounds of missile firings. Its latest missiles were fired from a site near the north- eastern city of Hamhung yesterday, between 3.19pm and 4.05pm.
South Korea's Joint Chiefs of Staff said the military is "keeping close tabs on the situation and standing by with a heightened defence posture".
Analysts said Pyongyang is using a combination of provocations and threats to protest against international pressure on the regime. This includes the latest and toughest UN sanctions imposed on the North in retaliation for its nuclear test, unilateral sanctions announced by the US, South Korea and Japan, as well as the annual US-South Korea joint military exercises that are ongoing.
This time, there is the added pressure on the Kim Jong Un regime to demonstrate its power ahead of a major party congress due in May, said Dr Chung Eun Sook from the Sejong Institute think-tank.
The spate of missile launches has added urgency to an upcoming nuclear summit in Washington that will see world leaders discussing nuclear non-proliferation.
Dr Chung said the topic of denuclearising North Korea will definitely come up, but the talks might end up driving North Korea further into self-imposed isolation.
"In the last two decades, North Korea has consistently challenged international norms and demonstrated gestures for talks and dialogue from time to time. But ultimately, they will make excuses to justify their exit from dialogue," she said.