News of the call for "full combat posture" by Kim Jong Un follows a USA announcement that it had seized a large North Korean cargo ship for carrying an illegal shipment of coal.
Some observers say the North could fire more missiles, including those of a medium range, to up the pressure on the United States.
South Korea's military said more than 20 different kinds of 240 fragments of personal belongings and military gear were found on the site.
U.S. President Donald Trump said on Thursday the U.S. was looking very seriously at the DPRK's latest missile launch.
Just a few days ago, North Korea conducted a military exercise during which several missiles were fired, including short-range missiles according to experts.
South Korea's military says North Korea has fired at least one unidentified projectile from its western area.
It is Biegun's first visit to Seoul since Trump's February summit with Kim in Hanoi collapsed without a deal on rolling back Pyongyang's nuclear program. It did not give more details but said is working with the U.S to determine details.
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Kang said the DPRK's recent projectile launches were an act that is of no help for the improvement of inter-Korean relations and efforts to defuse military tensions on the peninsula, expressing her worry about it.
Michael Elleman, a missile defense expert at the International Institute for Strategic Studies, wrote in a piece for North Korean specialty site 38 North that the weapon bore similarities to a Russian ballistic missile called Iskander.
If the projectiles are confirmed to be ballistic missiles, the incident is likely to aggravate the impasse in nuclear negotiations, as the North is banned from launching any ballistic missiles under UN Security Council resolutions.
Since 2011, CASIC has been the major source of North Korea's large 16-wheel and 18-wheel TELs which carry its Hwasong-14 and Hwasong-15 liquid-fueled intercontinental ballistic missiles (ICBMs) aimed at the United States.
"Based on our comprehensive analysis of the information, the government believes the projectiles launched by North Korea on Thursday were short-range ballistic missiles", Iwaya added.
Thursday's launch was the North's second weapons test in less than a week, amid tensions with the U.S. over their fitful drive to reach an agreement under which North Korea would give up its nuclear weapons.
"I don't think we should get too excited about a short-range test unless someone can tell us that it was a long-range test that failed", Ganyard said.
Japan's defence ministry said it had not detected any ballistic missile in its territorial waters or exclusive economic zone and saw no direct impact on security. Cha said North Korea won't likely fire longer-range missile, such as its Hwasong-12 intermediate range missiles and Hwasong-14 and - 15 intercontinental ballistic missiles (ICBMs), unless it intends to abandon diplomacy for good as it's certain to invite fresh United Nations sanctions. "And also to stabilise this situation as soon as possible by completing, in the near future, a comprehensive plan of action on denuclearization and reciprocal measures, that both the United States and North Korea will be ready to accept, so that Pyongyang can return to denuclearisation talks", Cheong Seong-Chang concluded.