Chinese Foreign Minister Yang Jiechi summoned the DPRK ambassador in Beijing, Ji Jae-ryong, and urged his country to return to the track of "dialogue and negotiation".

A statement from China's Foreign Ministry said Pyongyang's nuclear test was conducted "in disregard of the common opposition of the international community" and that "the Chinese government is firmly opposed to this act".

"We strongly urge the DPRK to honor its commitment to de-nuclearization and refrain from any move that may further worsen the situation," the ministry said.

US President Barack Obama in a statement on Tuesday called the DPRK's latest nuclear test a "highly provocative act" that threatens US security and international peace.

"The danger posed by North Korea's threatening activities warrants further swift and credible action by the international community. The United States will also continue to take steps necessary to defend ourselves and our allies," said Obama.

The DPRK confirmed on Tuesday that it successfully conducted its third underground nuclear test, according to the government's Korean Central News Agency. The test was carried out in Kilju County in North Hamkyung province, in a "safe and perfect" manner with a smaller nuclear bomb than in previous detonations, KCNA said.

The test site is about 100 kilometers from the China-DPRK border. Pyongyang conducted two underground nuclear tests in 2006 and 2009, both of which were denounced in resolutions by the United Nations Security Council.

Yu Meihua, director of the Center for Korean Peninsula Peace Studies under the China Reform Forum, said the situation has reached a critical point and that "symptoms and root causes" of regional tension must be addressed.

"The parties involved should persist in efforts to promote de-nuclearization of the Korean Peninsula, and Pyongyang's concerns on security should be considered," Yu said.

The latest test took place exactly three weeks after the unanimous adoption of UN Security Council Resolution 2087, which expressed the council's determination to take "significant action" in the event of a further DPRK nuclear test.

UN Secretary-General Ban Ki-moon issued a statement condemning Tuesday's underground nuclear test.

"It is deplorable that Pyongyang defied the strong and unequivocal call from the international community to refrain from any further provocative measures," his statement read.

Ban, a diplomat from the Republic of Korea, said he was "gravely concerned about the negative impact of this deeply destabilizing act on regional stability as well as the global efforts for nuclear nonproliferation".

Urging the DPRK to "reverse course and work toward de-nuclearization of the Korean Peninsula", the UN chief expressed confidence that the Security Council would remain united and take "appropriate action".

The 15-nation member council had an emergency meeting early on Tuesday in New York convened by Kim Sook, UN permanent representative from the Republic of Korea, which holds the presidency of the council for February.

In a statement following the closed-door consultations, the council noted its pledge last month - in response to a Dec 12 ballistic-missile test - to take "significant action" in the event of nuclear testing by Pyongyang.

"In line with this commitment and the gravity of this violation, the members of the Security Council will begin work immediately on appropriate measures in a Security Council resolution," the council said on Tuesday.

The DPRK, however, vowed to continue with nuclear tests that it says target the United States - its "sworn enemy" - after the council's adoption of Resolution 2087 on Jan 22.

The December test involved the launch into orbit of an Earth-observation satellite, according to KCNA. International observers, including UN member governments, classified the launch as involving a ballistic missile.

Susan Rice, the US permanent representative to the UN, said that while technical details of Tuesday's test hadn't been released, it was clear that the DPRK is "a threat to regional peace and security, international peace and security".

"They are not acceptable, they will not be tolerated and they will be met with North Korea's increasing isolation and pressure under United Nations sanctions," Rice told reporters after the council meeting.

Bruce Klingner, a senior research fellow for Northeast Asia at the conservative Heritage Foundation in Washington, said the DPRK had again defied the UN and recent efforts by China to "prevent its troublesome neighbor from ratcheting up tension on the Korean Peninsula".

"Kim Jong-un has shown himself to be no less belligerent and dangerous than his predecessors," Klingner said, referring to the country's leader.

"Kim is also clearly willing to risk incoming South Korean President Park Geun-hye's nascent efforts to re-engage North Korea, just as Kim Jong-il rejected President Obama's similar attempts in 2009," the analyst said.

"Attention will now turn to Washington to see if the Obama administration lives up to its promise of significant repercussions for Pyongyang so blatantly and quickly disregarding the latest UN resolution," Klingner added.

Huang Youfu, professor of Korean studies at the Minzu University in China, said escalating regional tension was brought about by various negative factors that have "piled up". Miscalculations by relevant parties have contributed to the situation, he said.

Park, elected in December as the first female president of the Republic of Korea, strongly condemned the nuclear test, saying her government, which takes office on Feb 25, won't tolerate a nuclear-armed DPRK, her spokeswoman said.

Japan's Prime Minister Shinzo Abe called Pyongyang's nuclear test "regrettable" and said his government was considering unilateral sanctions against the DPRK.

Lu Chao, a specialist in Korean Peninsula studies at Liaoning Academy of Social Sciences, said mounting opposition from the international community will step up pressure on Pyongyang.

With the nuclear test done, all previous efforts by Washington, Tokyo and Seoul to communicate with Pyongyang have been negated and they would have to start from scratch, Lu said.

The Six-Party Talks, which bring together the Republic of Korea, the DPRK, China, the US, Japan and Russia, remain the most likely forum for trying to ease tensions. The talks began in 2003 but stalled in late 2008. The DPRK quit the discussions in April 2009 to protest international condemnation of its long-range missile tests.

yuweizhang@chinadailyusa.com and chenweihua@chinadailyusa.com