World leaders on Friday spoke of further sanctions against North Korea in reaction to the Stalinist country's announcement of carrying out its fifth nuclear test.
The UN Security Council, which held an emergency meeting, condemned the test, which was carried out in defiance of previous UN resolutions, and vowed to take "further significant measures."
"In line with the ... gravity of the violation, the members of the Security Council will begin to work immediately on appropriate measures," said Gerard van Bohemen, New Zealand's UN ambassador and current council president.
Samantha Power, US ambassador to the UN, warned that North Korea's latest nuclear test showed that the country was "seeking to perfect its nuclear weapons ... so they can hold the region and the world hostage."
Power's Chinese counterpart, Liu Jieyi, told reporters that it was "more urgent than ever to work together" to create a nuclear-free Korean Peninsula. However, he did not say whether his country, North's Korea's sole ally, would support further sanctions.
Possible steps against North Korea could include a call for a full implementation of existing measures, adding new names to the sanctions list or strengthening the current sanctions regime, said Matthew Rycroft, British ambassador to the UN.
UN Secretary General Ban Ki-moon urged the council to stand united, warning, "We must urgently break this accelerating spiral of escalation."
Meanwhile, US President Barack Obama agreed with South Korean and Japanese leaders to push existing measures against North Korea and "to take additional significant steps, including new sanctions, to demonstrate to North Korea that there are consequences to its unlawful and dangerous actions."
He condemned the North Korean test as "a grave threat to regional security and to international peace and stability."
Obama called the test a "flagrant violation" of Security Council resolutions that demonstrates North Korea "has no interest in being a responsible member of the international community."
Russia, in earlier condemning the nuclear test, also called for strict application of UN sanctions on North Korea.
Tension has been high since North Korea's fourth nuclear test in January and a controversial rocket launch in February, events which led the Security Council to tighten economic sanctions on the isolated nation.
The council again condemned Pyongyang on Tuesday, a day after it fired three ballistic missiles into the Sea of Japan, coinciding with a G20 summit in the Chinese city of Hangzhou.
Friday's test showed "sanctions are not working in terms of constraining North Korea's nuclear capabilities,” said Shannon Kile, nuclear weapons researcher with the Stockholm International Peace Research Institute (SIPRI).
"We are simply going to have to recognize that North Korea is a nuclear weapon state. It de facto possesses them and is not going to give those weapons up. The international community and the regional powers probably have to come up with other approaches," Kile told dpa.
In Vienna, the Comprehensive Nuclear-Test-Ban Treaty Organization said it may take several days to confirm that North Korea carried out a nuclear test.
The first sign of the test was a magnitude-5 earthquake located near North Korea's Punggye-ri underground nuclear test site, where all of the country's tests have taken place since the first test in 2006 and where recent satellite imagery had shown fresh activity.
South Korea's joint chiefs of staff said the test, which coincided with the 68th anniversary of the founding of Pyongyang regime, was likely the North's "biggest ever."
The yield was thought to have been 10 kilotons, South Korea's Yonhap news agency reported. The bomb dropped by US forces on Hiroshima in 1945 had a yield of 16 kilotons.
North Korea's atomic authority said the test had been of a nuclear warhead that could be mounted on a ballistic missile and that it was now in a position to produce many "smaller, lighter and diversified" nuclear weapons, the state-run KNCA news agency reported.
China expressed "firm opposition" to Pyongyang's nuclear test.
"We strongly urge [North Korea] to honour its commitment to de-nuclearization, comply with relevant Security Council resolutions, and take action to stop the deterioration of the situation," the Foreign Ministry said.
US Secretary of Defence Ashton Carter said the test "is another destabilizing and provocative act."
"We need to redouble the pressure on North Korea," Carter told reporters Friday after completing a visit to Norway.