International reaction

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!"

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.

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."

China, North Korea's closest ally, urged restraint.

"The situation on the Korean Peninsula is sensitive and complex," Ministry of Foreign Affairs spokesman Geng Shuang said. "We hope all relevant parties will exercise restraint and avoid taking actions that may escalate tensions."

South Korean President Moon Jae-in warned North Korea not to cross the "bridge of no return" and called on China to play a stronger role in resolving the situation.

Nikki Haley, the US ambassador to the United Nations, told Chinese Ambassador Liu Jieyi, president of the UN Security Council, that she wants an emergency session on North Korea, according to a tweet from Haley spokesman Jonathan Wachtel.

The emergency session will convene Wednesday afternoon, Wachtel wrote.

UN Secretary-General António Guterres strongly condemned the missile test.

"This action is yet another brazen violation of Security Council resolutions and constitutes a dangerous escalation of the situation," Guterres said through his spokesman Stephane Dujarric. "The DPRK leadership must cease further provocative actions and comply fully with its international obligations."

Most successful test yet

A Japanese defense official said North Korea's missile, referred to as Hwasong-14 on state TV, flew into waters east of the Korean Peninsula and may have landed in Japan's exclusive economic zone, which extends 200 nautical miles from its coastline.

The US Pacific Command said it tracked the missile for 37 minutes and described it as a "land-based, intermediate range ballistic missile." Japan reported that its flight time was 40 minutes.

South Korea said the missile had an "improved range" compared with the May launch.

'One successful test doesn't get them over the bar'

But one apparently successful test doesn't necessarily mean that North Korea has the global capability it claimed, said Euan Graham, director of the international security program at Sydney's Lowy Institute for International Policy.

"If the North Koreans are claiming they can launch an ICBM (to) anywhere in the world, that needs to be looked at through a technical lens," he said.

"One successful test doesn't get them over the bar; they're claiming more than they can deliver at the moment."

Bruce Bennett, senior international/defense researcher at RAND Corp., said North Korea had aimed high to limit the distance traveled and avoid a major international incident.

"You can't hardly fire a missile from North Korea that's got a thousand-kilometer range without it going into somebody's exclusive economic zone. The bottom line is, they've flown it very high so that they can test the range of the missile," Bennett said.

"If they were to shoot it on a normal trajectory, it's probably going to go out 6,000 or so kilometers. By definition, anything over 5,500 kilometers is an ICBM."

Russia, which shares a small border with North Korea, cast doubt on Pyongyang's assertion that an ICBM was fired.

The Russian Defense Ministry said it believed the missile reached an altitude of 535 kilometers (332 miles) and traveled 510 kilometers (317 miles), according to the state-run news agency Sputnik.

"The parametric data of the ballistic target's trajectory matches the performance characteristics of a medium-range ballistic missile," the ministry said.

Melissa Hanham, a senior research associate at the James Martin Center for Nonproliferation Studies, said an ICBM test would put the United States in a difficult negotiating position.

"I think there's room for negotiation, but it's not the kind of negotiations we want," Hanham said.

The United States can now only work toward limiting, not eliminating, the North Korean missile threat to the US mainland, she said.