Tokyo: North Korea's neighbours lined up on Wednesday to condemn Pyongyang's claimed hydrogen bomb test, saying it posed a grave threat to regional security.
Several governments promised a firm response as tensions soared again in northeast Asia, many calling for further action by the United Nations against the hermit nation, which is already subject to heavy international sanctions.
The United Nations Security Council will hold an emergency meeting on Wednesday in New York. The closed-door morning talks between the 15 member nations were called by the United Nations and Japan.
India reacted to North Korea's test, with a statement from the External Affairs Ministry saying:
"We have seen reports that DPRK has conducted a nuclear test today. We are assessing the available information, including claims that this was a thermonuclear test. It is a matter of deep concern that DPRK has again acted in violation of its international commitments in this regard. We call upon DPRK to refrain from such actions which adversely impact on peace and stability in the region. Our concerns about proliferation links between North East Asia and our neighbourhood are well-known."
Japan's Prime Minister Shinzo Abe said, "The nuclear test that was carried out by North Korea is a serious threat to the safety of our nation and we absolutely cannot tolerate this."
"This clearly violates UN Security Council resolutions and is a grave challenge against international efforts for non-proliferation," he said, adding his country would seek to coordinate efforts among UN members to deal with the action.
South Korean President Park Geun-Hye called the test a "grave provocation" at an emergency meeting of the Country's National Security Council (NSC) convened immediately after the news broke.
"The test is not only a grave provocation to our national security but also a threat to our future... and a strong challenge to international peace and stability," she said, calling for strong sanctions on Pyongyang.
In an earlier statement, Seoul said it would "take all necessary measures including additional sanctions by the UN Security Council... so that the North will pay the price for the nuclear test".
North Korea's main ally China also said that it "firmly opposes" Pyongyang's purported hydrogen bomb test and is monitoring the environment along its border with the North near the test site.
China plans to summon North Korea's ambassador in Beijing to the Foreign Ministry to lodge a strong protest, spokeswoman Hua Chunying told reporters at a daily briefing Wednesday. China made a similar protest after the North's last nuclear test in 2013.
Wednesday's reported test was performed in defiance of the international community and in contravention of its earlier denuclearization promises, Hua said.
"North Korea should stop taking any actions which would worsen the situation on the Korean peninsula," Hua said.
Environment bureau technicians were monitoring conditions near the border but air quality near the bomb site was within the normal range, Hua said.
In the longer term, North Korea should return to long-stalled six-nation denuclearization talks hosted by China, Hua said. North Korea abandoned that process in 2009, saying it would continue its nuclear program to produce a deterrent against alleged threats from the U.S. and other enemies.
While she made no mention of measures to respond to a test, analysts say Pyongyang's proceeding against Beijing's objections would seriously harm a relationship already under considerable strain.
That will likely include agreeing to tougher UN sanctions against Kim Jong Un's hard-line communist regime and possibly unilateral trade restrictions that could hurt the North's moribund economy.
Despite that, China remains the North's most important ally and trade partner.
In Washington, the White House would not confirm the test, but vowed to "respond appropriately to any and all North Korean provocations".
There was no immediate response from China, North Korea's key diplomatic protector, but in a report from Pyongyang, the official Xinhua news service said that the "test apparently runs counter to relevant UN resolutions" and "is set to cause repercussions".
Russia also slammed the test as a clear breach of international law that could enflame tensions across the region.
"If this test is confirmed then it will be a new step by Pyongyang on the path of developing nuclear weapons, which is a flagrant violation of international law and existing UN Security Council resolutions," Russia's foreign ministry said in a statement.
The European Union called it a "grave violation" of a UN ban on its development of nuclear weapons and a threat to the region.
"If confirmed, this action would represent a grave violation of (North Korea's) international obligations not to produce or test nuclear weapons, as determined by several United Nations Security Council Resolutions, and a threat to the peace and security of the entire northeast Asia region," EU foreign affairs head Federica Mogherini said in a statement.
France also slammed North Korea's testing of a nuclear bomb as an "unacceptable violation" of UN Security Council resolutions and called for a "strong reaction from the international community".
"While awaiting confirmation of the characteristics of the nuclear test announced and observed last night in North Korea, France condemns this unacceptable violation of (UN) Security Council resolutions and calls for a strong reaction from the international community," the presidency said in a statement.
Australian foreign minister Julie Bishop said her country "condemns in the strongest possible terms" the test, which "confirms North Korea's status as a rogue state and a continuing threat to international peace and security", adding that Canberra would express its concerns to Pyongyang directly and call for stronger UN sanctions.
The test, which came just two days before leader Kim Jong-Un's birthday, was initially detected by international seismology monitors as a 5.1-magnitude tremor next to the North's main Punggye-ri nuclear test site in the northeast of the country.
Last month, North Korean leader Kim Jong-Un suggested Pyongyang had already developed a hydrogen bomb.
The claim was questioned by international experts and there was continued scepticism over today's test announcement.
With agency inputs