Russia and China have urged North Korea to "freeze" its missile and nuclear programmes after it claimed to have successfully tested its first intercontinental ballistic missile.
Meanwhile, US officials reportedly said they believed North Korea's claim.
But while Pyongyang appears to have made progress, experts believe the device cannot accurately hit a target.
Calling the launch "unacceptable", Russia and China, which share a land border with North Korea, also urged the US to not deploy the Thaad missile system - which aims to intercept attacks from Pyongyang - in South Korea.
Chinese President Xi Jinping was in Moscow, where he held talks with Russian President Vladimir Putin.
What North Korea say?
The announcement on North Korea state television said the Hwasong-14 intercontinental ballistic missile (ICBM) test was overseen by leader Kim Jong-un.It said the projectile had reached an altitude of 2,802km (1,731 miles) and flew 933km for 39 minutes before hitting a target in the sea.
North Korea, it said, was now "a full-fledged nuclear power that has been possessed of the most powerful inter-continental ballistic rocket capable of hitting any part of the world".
The launch, the latest in a series of tests, was in defiance of a ban by the UN Security Council.
But experts also believe that Pyongyang does not have the capacity to miniaturise a nuclear warhead that can fit onto such a missile.
How far could this missile travel?
The big question is what range it has, says the BBC's Steven Evans in Seoul. Could it hit the United States?David Wright, a physicist with the US-based Union of Concerned Scientists, says that if the reports are correct, this missile could "reach a maximum range of roughly 6,700km on a standard trajectory".
That range would allow it to reach Alaska, but not the large islands of Hawaii or the other 48 US states, he says.
Unnamed US officials told media that they believed the test was of an ICBM, with one authority saying that the claim was being "taken seriously".
National security, military and diplomatic officials were discussing what to do if it is determined for certain that the test was with an intercontinental ballistic missile, CNN reported.