An official from Pyongyang has reportedly said his country is planning to conduct a third nuclear test in the coming week, a news report said on Saturday.

But the Chinese Foreign Ministry told China Daily on Sunday it was "not aware" of such plans.

Joongang Ilbo Daily in Seoul quoted an unidentified official from the Republic of Korea as saying that he had heard a Democratic People's Republic of Korea official in Beijing say that "Pyongyang plans to carry out a nuclear test between Sunday and Jan 20".

"We are increasing our surveillance of the Punggye-ri nuclear test site," the official said in reference to the DPRK's only nuclear test site, where tests were conducted in 2006 and 2009.

The report cited sources as saying that the nuclear test is to help make smaller and lighter nuclear warheads.

With the UN Security Council still debating possible sanctions against Pyongyang after the launch of a long-range rocket last month, there has been widespread speculation that the DPRK may carry out a third nuclear test.

A US think tank, citing satellite images, said last month that Pyongyang had repaired extensive rain damage at the nuclear test site in the northeast of the country and can detonate a nuclear bomb on two weeks' notice.

The US-Korea Institute at Johns Hopkins University said satellite photos from Dec 13 showed Pyongyang was determined to maintain a state of readiness at Punggye-ri nuclear test site.

The ROK's Unification Minister Yu Woo-ik told a parliamentary committee last month it was "highly probable" that the DPRK would follow up the successful rocket launch with another nuclear test. "Judging from analysis of intelligence data, significant preparations have been made," he said.

However, Yang Moo-jin, a professor at the University of North Korean Studies in Seoul, said there were "no signs that a nuclear test is imminent".

"Chances are slim that Pyongyang would push ahead with a nuclear test this winter, especially when China is insisting on a moderate response to the rocket launch to prevent a third nuclear test taking place," Yang told AFP.

Joongang Ilbo Daily said the test would cloud the new ROK administration's policies toward Pyongyang.

ROK's President-elect Park Geun-hye has sought a change in the relations, yet has vowed to stay firm on the issue of Pyongyang's nuclear weapons.

She told China's visiting Vice-Minister of Foreign Affairs Zhang Zhijun on Thursday that the DPRK's nuclear weapon development "can never be tolerated".

The report also said a nuclear test right on the heels of the debated rocket launch will further worsen Pyongyang's international relations.

"So it might be very prudent to decide whether to go on with the provocations after observing the overall framework of the new ROK government's policies toward Pyongyang," the report said.

Pyongyang's previous nuclear tests were both carried out within months of long-range rocket launches.

The DPRK says that the launch was a purely scientific mission to put an observation satellite in polar orbit, but some other countries claim it was a disguised ballistic missile test.

China Daily-AFP