The missile flew about 60km before hitting the water, according to the South Korean military.
A White House official also said on Tuesday that "all options are on the table" for the United States, though the official would not say what steps Trump was willing to take to curb dictator Kim Jong-un's pursuit of a nuclear weapon.
China is North Korea's sole major diplomatic friend and a key trading partner that supplies the isolated state with much of its hard currency in the face of stringent global sanctions.
"The military is keeping a close watch over North Korea's provocative moves and maintaining a high defense posture", it said. But he also said the missile launch was hard to understand because North Korea benefits from the US and China being at odds with one another.
"The North American Aerospace Defense Command determined the missile launch from North Korea did not pose a threat to North America", said Cmdr.
During a military parade in April 2012, North Korea's military displayed a mockup of a mobile ICBM system referred to as the Hwasong-13 (designated by the United States as the KN-08).
The hardened US stance followed recent North Korean missile launches that Pyongyang described as practice for an attack on USA bases in Japan. The missile launch may be a precursor, with more to come as the summit starts Thursday, he said.
Weather Service confirms Cleburne County tornado
The National Weather Service has issued a tornado watch for the Hampton Roads region on Thursday morning. Vincent's Academy sent students home at 1 p.m. because of the potential for severe weather.
Two weeks ago, the South Korean and US militaries said they had detected a failed North Korean ballistic missile launch.
President Donald Trump had warned on Sunday in an interview with Financial Times that he could take unilateral action to eliminate North Korea's nuclear threat.
South Korea's Foreign Ministry called the North's latest missile launch a "reckless provocation" that posed a threat to worldwide peace, while Japan's Chief Cabinet Secretary Yoshihide Suga said the country lodged a strong protest over the launch.
This year, North Korea officials, including young leader Kim Jong Un, have repeatedly indicated an ICBM test, or something similar, could be coming, possibly as soon as April 15, the 105th birthday of North Korea's founding president and celebrated annually as "the Day of the Sun".
Trump has said China must do more to pressure North Korea to halt its nuclear and missile programs.
The 60 kilometers is a relatively short flight compared with the distances that other North Korean missiles flew.
The launch was North Korea's latest in a long series of missile and nuclear tests that have accelerated in their variation and intensity over the last two years. On March 6, Pyongyang fired four medium-range ballistic missiles from Tongchang-ri region - near the border with China - toward the Sea of Japan, three of which fell in Japan's exclusive economic zone. North Korea sees the drills as an invasion rehearsal. This is the second launch of a KN-15 (called the Pukguksong-2 by North Korea), and it raises concerns that the North Korean regime may be working on a solid-fuel intercontinental ballistic missile (ICBM).