Russia's foreign ministry has expressed "strongest condemnation" of North Korea's announcement that it had tested a hydrogen bomb Sunday.
Russai however called for calm in order for the matter not to grow out of proportion.
it is imperative to remain calm and to refrain from any actions that lead to a further escalation of tension.
The ministry said it regretted that the leadership of North Korea was "creating a serious threat" for the region and warned that "the continuation of such a line is fraught with serious consequences" for Pyongyang.
Japanese Prime Minister Shinzo Abe slammed the test as "absolutely unacceptable" and said North Korea's nuclear and missile programmes now pose a more "grave and urgent" threat to his country.
Whether we can stop North Korea's reckless actions that threaten world peace depends on the cooperation and solidarity of the international community.
French President Emmanuel Macron also called for a "very firm" response by the international community and urged the UN Security Council to "quickly react".
EU foreign policy chief Federica Mogherini said she was looking forward "to the UN Security Council addressing the matter and taking a firm and effective stand".
NATO secretary general Jens Stoltenberg condemned the test as "yet another flagrant violation" of multiple UN Security Council resolutions.
NATO is concerned by Pyongyang's destabilising pattern of behaviour, which poses a threat to regional and international security.
Pyongyang, for its part, called the nuclear detonation "a perfect success".
According to US monitors, the test was substantially larger than previous ones, generating a 6.3 magnitude earth tremor.
Washington has not responded so far.
After North Korea sent a missile over Japan last week, Trump tweeted that the time for talks was over.
The US has been talking to North Korea, and paying them extortion money, for 25 years. Talking is not the answer!
Trump had previously pledged the North would not get an ICBM and has warned that Washington's weapons are "locked and loaded".topics from