China said it strongly opposes Pyongyang's third nuclear test conducted on Tuesday, and observers are calling for calm and restrain among all parties to avoid aggravating an already tense situation.

The Democratic People's Republic of Korea said on Tuesday it has successfully conducted the third underground nuclear test, according to the official KCNA news agency. The test was carried out in Kilju County of North Hamkyung Province, and was done in a "safe and perfect" way with a smaller A-bomb unlike previous ones, the KCNA said.

The test site is about 100 km from the China-DPRK border.

A statement by the Chinese Foreign Ministry said the nuclear test was conducted "in disregard of the common opposition of the international community", and "the Chinese government is firmly opposed to this act".

"We strongly urge the DPRK to honor its commitment to denuclearization and refrain from any move that may further worsen the situation," it said.

Foreign Minister Yang Jiechi on Tuesday also summoned the DPRK ambassador to China, Ji Jae-ryong. He urged Pyongyang to return to the track of dialogue and negotiation.

A commentary by China's official news agency Xinhua said it has come to a point for parties concerned to act rationally to create favorable conditions to revive long-stalled Six-Party Talks and "avoid a disastrous fallout".

Yu Meihua, director of the Center for Korean Peninsula Peace Studies under the China Reform Forum, said the situation has come to a critical point, and a strong recipe is needed to deal with both the "symptoms and root causes" of the issue.

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

Pyongyang conducted two nuclear tests in 2006 and 2009. Both tests were denounced by UN Security Council resolutions.

The test on Tuesday was conducted after the DPRK on Jan 23 declared an end to any efforts of denuclearizing the Korean Peninsula, hours after the UN Security Council adopted a resolution condemning its rocket launch on Dec 12.

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

The Republic of Korea's president-elect Park Geun-hye strongly condemned the nuclear test, saying the incoming government will not tolerate a nuclear-armed DPRK, her spokeswoman said.

US President Barack Obama condemned the nuclear test as "highly provocative", and urged "further swift and credible action" by the international community.

Japanese Prime Minister Shinzo Abe said that the nuclear test is regrettable, and his government is mulling unilateral sanctions on the DPRK.

Earlier in the day, KCNA said Pyongyang vowed to proceed with missile and nuclear tests targeting the United States, its "sworn enemy", after the UN Security Council adopted a resolution to condemn its Dec 12 rocket launch.

Lu Chao, a specialist of Korean Peninsula studies at the 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 ROK, the DPRK, China, the US, Japan and Russia, remain the most viable platform to reverse hostilities, Xinhua said. The talks had begun in 2003 but stalled in December 2008. The DPRK quit the talks in April 2009 in protest against international condemnation of its long-range missile tests.

Xinhua contributed to this story.

zhangyunbi@chinadaily.com.cn