North Korea on Friday fired a medium-range ballistic missile into the sea, days after its leader Kim Jong Un ordered tests likely aimed at developing technology it needs to acquire to build a missile capable of reaching the U.S. mainland.South Korea's Joint Chiefs of Staff said in a statement that the missile flew 800 kilometers (500 miles) before crashing off the North's east coast on Friday.South Korean military officials said it wasn't immediately known what type of missile was fired. But a South Korean defense official, requesting anonymity citing department rules, said it is the first medium-range missile launched by the North since April 2014 when it fired two.A senior U.S. defense official said the Pentagon can confirm that North Korea conducted a ballistic missile launch into the Sea of Japan. The official said it appears to have been a Nodong medium range ballistic missile launched from a road-mobile transporter erector launcher.He said test represents a violation of multiple UN Security Council resolutions.Friday's launch came amid a heightened international standoff over the North's weapons programs in the wake of its nuclear test and long-range rocket launch earlier this year.In recent weeks, North Korea threatened pre-emptive nuclear strikes against Washington and Seoul and test-fired short-range missiles and artillery into the sea in response to tough U.N. sanctions imposed over its nuclear test and rocket launch. The North says it needs nuclear weapons to cope with what it calls U.S. military threats.On Tuesday, North Korea's state media said Kim had ordered tests of a nuclear warhead and ballistic missiles capable of carrying warheads. Kim issued that order while overseeing a successful simulated test of a re-entry vehicle aimed at returning a nuclear warhead into the atmosphere from space so it could hit its intended target.This led South Korean analysts to suspect that the North would likely fire a missile soon to test the re-entry technology.Some analysts had also predicted the North might fire a missile carrying an empty warhead, which contain trigger devices but lack plutonium or uranium, to see if those warhead's parts can survive the high pressure and temperatures upon re-entry into the atmosphere and if they were able to detonate at right time.Outside experts said it is the last major technology that North Korea must master to achieve its goal of developing a long-range missile capable of hitting the U.S. mainland.South Korean defense officials said North Korea hadn't yet to acquire the re-entry technology so that it doesn't yet have a functioning intercontinental ballistic missile.