North Korea appears technically ready to conduct its fourth nuclear test any time once a political decision is made, South Korea's foreign minister said Thursday.

Concerns have been growing since Pyongyang threatened to conduct a "new form" of nuclear test late last month. South Korean officials are on alert after detecting "increased activity" at North Korea's Punggye-ri nuclear test site in its mountainous northeastern region close to its border with China and Russia.

North Korea has so far carried out nuclear tests in 2006, 2009 and 2013.

"If there's a political decision made, (North Korea) seems to be technically prepared to carry out a nuclear test any time," Foreign Minister Yun Byung-se said in a meeting of the National Assembly's foreign affairs committee.

"We have gathered (information) that various activities (related with a nuclear test) are taking place more actively," Yun said, repeating the defense ministry's similar announcement earlier this week.

Yun said South Korea is now in close contact with the United States and China to block the possible nuclear test, pledging to take stern counteractions if the North carries out the test.

"The key members of the international community, including the U.S. and China, are having in-depth consultations" over the possible nuclear test, Yun noted.

"The international community is of the same voice that North Korea's fourth nuclear test will be a very serious (issue). If the North goes ahead with a test in defiance of the international warnings, it will face painful measures."

On Thursday, Choson Sinbo, a pro-Pyongyang newspaper published in Japan, argued that Seoul's talk of an imminent nuclear test by it is an attempt to shift public attention away from the deadly sinking of a ferry off South Korea's southwest coast last week.

"The talk about North Korea's nuclear test is being handed out by the South Korean government over to the media and it's one of the makeshift crisis control tricks aimed at taking people's attention to elsewhere," said the newspaper in a report.

But it was not clear whether the newspaper article indicates North Korea's dismissal of the widespread speculation of the possible additional nuclear test.

Ahead of its last nuclear test in February 2013, the North similarly criticized reports of the growing likelihood of a new nuclear test.  (Yonhap)