North Korea appears to have fired missile that may have landed in Japan's territorial waters - Japanese media has revealed.
The missile appeared to land in the sea off Japan, the Japanese national broadcaster NHK said.
In early July, Pyongyang claimed to have successfully tested an intercontinental ballistic missile (ICBM) for the first time.
That test was the latest in a series conducted in defiance of a UN ban. The range of the latest test is not known.
The range of North Korea's ICBM has been disputed, but some experts said it could reach Alaska.
Pentagon spokesman Captain Jeff Davis said a launch appeared to have been conducted and that more information was awaited.
The latest missile test is the 14th test carried out by North Korea in 2017.
The missile was launched at 23:41 North Korea time (15:41 GMT) from Jagang province in the north of the country, South Korean news agency Yonhap reported.
Japanese Chief Cabinet Secretary Yoshihide Suga said the missile flew for about 45 minutes - slightly longer than the ICBM tested in July.
He said it landed in the sea in Japan's exclusive economic zone - not within Japan's territorial waters.
South Korea's President Moon Jae-in has convened an emergency security meeting for the middle of the night, Yonhap said.
However, earlier this month North Korea claims to have conducted its first successful test of a long-range missile that it says can "reach anywhere in the world."
The missile test reached a height of 2,802 kilometers (1,741 miles), according to state broadcaster Korea Central Television, which would be the highest altitude a North Korean missile had ever reached.
The country claimed it was an intercontinental ballistic missile, or ICBM, which would put the United States on notice that Pyongyang could potentially hit the US mainland.
US military analysts believe it probably was a two-stage ICBM, said a US official with knowledge of the Americans' analysis.
North Korea appears to have timed the launch for maximum political effect, giving the order to fire on the eve of the July Fourth holiday, just days after President Donald Trump spoke with Japanese and Chinese leaders about the North Korean threat and before this week's G20 meeting.
The fear is that North Korea may one day develop the technology to mount a miniature nuclear warhead on a long-range missile, something analysts say it may have already achieved.
Trump's reaction to the launch was scathing. "North Korea has just launched another missile. Does this guy have anything better to do with his life?" Trump asked on Twitter, referring to North Korean leader Kim Jong Un.
"Hard to believe that South Korea and Japan will put up with this much longer. Perhaps China will put a heavy move on North Korea and end this nonsense once and for all!"
....and Japan will put up with this much longer. Perhaps China will put a heavy move on North Korea and end this nonsense once and for all!
US national security, military and diplomatic officials were holding an unplanned meeting Tuesday to discuss US options if it determines North Korea did test an ICBM, several administration officials said.
If it was an ICBM, Trump could approve a "measured response," one official told CNN. Nothing has been decided, but such a response could include sending additional US military assets to the region and diplomatic efforts such as more sanctions, the official said.
What does Trump do now?
US military analysts initially thought North Korea launched an intermediate, single-stage missile, the source familiar with the American analysis said. But further examination revealed a second-stage booster may have ignited, producing 30 seconds of additional flight, the source said.
President Vladimir Putin said Russia would work with China to resolve the crisis. At a joint news conference Tuesday in Moscow with Chinese President Xi Jinping, Putin said: "It is very important to push forward our joint initiative on settling the Korean problem with a view of immediately freezing the ballistic missile strikes and also dealing with the US deployment of weapons in South Korea."