North Korea launched what appeared to be a second intermediate-range Musudan missile on Wednesday morning after another launch hours earlier failed, South Korea's military said.
It was not immediately clear if the second launch, about two hours after the first, was successful.
The first missile was launched from the east coast city of Wonsan, a South Korean official said, the same area where previous tests of intermediate-range missiles were conducted, possibly using mobile launchers.
The launches were in continued defiance of international warnings and a series of U.N. Security Council resolutions that ban the North from using ballistic missile technology, which Pyongyang rejects as an infringement of its sovereignty.
Japan said after the first launch that it would protest strongly because it violated a United Nations resolution, Kyodo news agency reported, citing a government statement.
Japanese Defense Minister Gen Nakatani told reporters after the launch that there had been no effect on Japan's security. The Kyodo news agency separately quoted Nakatani as saying it was a “grave provocative action."
The U.S. military detected a missile launch from North Korea, Navy Commander Dave Benham, a spokesman from the U.S. military's Pacific Command, told Reuters in Washington on Tuesday after the first launch without providing details.
The first missile failed in flight over the sea between the Korean peninsula's east coast and Japan, according to initial indications after the launch, said another U.S. official who also said it was likely to have been another Musudan.
The failure, if confirmed, would be the fifth straight unsuccessful attempt in the past two months to launch a missile that is designed to fly more than 3,000 km (1,800 miles) and could theoretically reach any part of Japan and the U.S. territory of Guam.
Japan put its military on alert on Tuesday for a possible North Korean ballistic missile launch and South Korea's Yonhap News Agency, citing an unidentified government source, said the North was seen to be moving an intermediate-range missile to its east coast.
North Korea is believed to have up to 30 Musudan missiles, according to South Korean media, which officials said were first deployed around 2007, although the North had never attempted to test-fire them until April.
The U.N. Security Council, backed by the North's main diplomatic ally, China, imposed tough new sanctions in March after the isolated state conducted its fourth nuclear test in January and launched a long-range rocket that put an object into space orbit.
North Korea has conducted a series of tests since then that it claimed showed progress in nuclear weapons and long-range ballistic missile capabilities, including new rocket engines and simulated atmospheric re-entry.