Seoul: North Korea appears to be preparing for a third nuclear test, a South Korean newspaper reported Thursday, just days after Pyongyang declared it was ready to return to nuclear talks.

But South Korean government officials said there was no concrete evidence that the communist state was readying such a test, saying Seoul and its allies are closely watching developments related to the North’s nuclear facilities.

According to South Korea’s biggest-selling newspaper Chosun Ilbo, US satellites detected movements of personnel and vehicles at the site where the the North carried out its first two nuclear tests in 2006 and 2009.

“Hectic movements of personnel and vehicles have recently been detected in Punggye-ri,” Chosun quoted an unidentified government source as saying.

The North also appears to be restoring tunnels demolished during the first two tests, according to the source.

“However, it is unlikely (the North will) carry it out soon. It is expected to take another three months (to complete preparations for a third test),” the source said.

But a spokesman for South Korea’s Joint Chiefs of Staff said there was no evidence of any such preparations.

“We have no concrete evidence to support the news report,” he told reporters. “We’re watching closely any development concerning the North’s nuclear facilities and sharing information with countries concerned.”

A South Korean defence ministry official also told AFP on condition of anonymity that such movements were being constantly detected, possibly for the daily maintenance of key strategic facilities at the site.

Another government source told Yonhap news agency that since the North’s last nuclear test in May 2009 there has been consistent movement of personnel and vehicles around Punggye-ri.

“It is difficult to regard these moves as signs that a nuclear test is imminent,” the source was quoted as saying by Yonhap.

North Korea conducted its first two nuclear tests, in October 2006 and May 2009, in Punggye-ri in the northeastern province of North Hamgyong, the second coming the month after it walked out of six-party nuclear disarmament talks.

The Chosun report came as Seoul is preparing to host a Group of 20 summit next month, welcoming world leaders including US President Barack Obama.

North Korea said on Saturday it was willing to resume the six-nation disarmament talks but would not be “hasty” because the United States and some other parties were “not ready”.

The United States says the North must mend relations with the South and show sincerity about nuclear disarmament before any resumption of the negotiations.

A senior South Korean foreign ministry official said Wednesday the North should allow inspectors back to its nuclear facilities and declare a moratorium on its nuclear activities before the six-party talks can resume.

The unidentified official also said Seoul’s proposal last year of a “grand bargain,” in which President Lee Myung-bak offered the North massive economic aid for complete denuclearisation, was still valid, Yonhap news agency said.

China, the North’s sole major ally and economic lifeline, is pressing to restart the six-party forum, which groups the two Koreas, the United States, China, Japan and Russia and began in 2003.

Prospects for renewed negotiations have been clouded by South Korean and US accusations that the North torpedoed one of Seoul’s warships in March, a charge Pyongyang denies.

The 1950-53 Korean War ended only in an armistice and without a formal peace treaty.