South Korean military officials say North Korea has fired a ballistic missile into the ocean off its eastern coast.
The U.S. military said it detected two simultaneous missile launches, one was successful and the other exploded immediately after launch.
Officials say the missile, believed to be a medium-range Rodong missile, was fired just before 8 a.m. Wednesday from Unyul in the country's western Hwanghae province and flew about 1,000 kilometers before landing in or close to Japanese waters.
Japanese Prime Minister Shinzo Abe called the missile launch a "grave threat" to Japan's security and expressed strong objections to the North's continued ballistic missile aspirations.
The United States immediately responded to the test Wednesday, warning the North Koreans that it is ready to defend itself and its allies from any provocation.
North Korea is seeking to develop a warhead small enough to be placed on a long-range missile that can reach the continental United States. But South Korean defense officials say Pyongyang does not yet have such a miniaturized warhead.