North Korea has said the missile it tested on Wednesday held a warhead capable of re-entering the Earth's atmosphere.
The claim was not proven and experts have cast doubt on the country's ability to master such technology, BBC reported on Wednesday.
North Korean Kim Jong-un called the launch "impeccable" and a "breakthrough". It was the first test from Pyongyang in more than two months, after a flurry earlier this year.
It has been condemned by the international community.
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US President Donald Trump spoke to China's President Xi Jinping by telephone, the White House said, urging him to "use all available levers to convince North Korea to end its provocations and return to the path of denuclearisation".
Xi responded by telling Trump it was Beijing's "unswerving goal to maintain peace and stability in north-east Asia and denuclearise the Korean peninsula".
China is North Korea's biggest ally and most important trading partner, and the two share a land border.
Experts say the height reached by the inter-continental ballistic missile (ICBM) indicates Washington could be within range, although North Korea is yet to prove it has reached its aim of miniaturising a nuclear warhead.
White House spokeswoman Sarah Sanders said the US would put more sanctions on North Korea "very shortly".
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The Hwasong-15 missile, described as North Korea's "most powerful", was launched in darkness early on Wednesday.
It landed in Japanese waters but flew higher than any other missile the North had previously tested.
The test, which defied international sanctions imposed over the North's weapons programme, drew swift international condemnation.
South Korea responded by launching one of its own ballistic missiles in a live-fire drill.
Pyongyang says the missile reached an altitude of 4,475 km and flew 950 km in 53 minutes. That huge altitude, sending it far outside Earth's atmosphere, is close to independent estimates made by South Korea's military.
The projectile, fired at a steep incline, did not fly over Japan as some have done in the past, and landed about 250 km short of its northern coast, according to Japanese officials.