SEOUL, South Korea - North Korea said Tuesday it would use nuclear weapons in a "merciless offensive" if provoked -- its latest rhetoric apparently aimed at deterring any international punishment for its recent atomic test blast.

The tensions emanating from Pyongyang are beginning to hit nascent business ties with the South: a Seoul-based fur manufacturer became the first South Korean company to announce Monday it was pulling out of an industrial complex in the North's border town of Kaesong.

The complex, which opened in 2004, is a key symbol of rapprochement between the two Koreas but the goodwill is evaporating quickly in the wake of North Korea's nuclear test on May 25 and subsequent missile tests.

Pyongyang raised tensions a notch by reviving its rhetoric in a commentary in the state-run Minju Joson newspaper Tuesday.

"Our nuclear deterrent will be a strong defensive means ... as well as a merciless offensive means to deal a just retaliatory strike to those who touch the country's dignity and sovereignty even a bit," said the commentary, carried by the official Korean Central News Agency.

It appeared to be the first time that North Korea referred to its nuclear arsenal as "offensive" in nature. Pyongyang has long claimed that its nuclear weapons program is a deterrent and only for self-defense against what it calls U.S. attempts to invade it.

The tough talk came as South Korea and the U.S. lead an effort at the UN Security Council to have the North punished for its nuclear test with tough sanctions.

South Korea's chief nuclear envoy Wi Sung-lac said Tuesday that the Security Council is expected to adopt a resolution on North Korea within a couple of days, the South's Yonhap news agency reported.

Wi arrived late Tuesday in Beijing for talks with top Chinese officials on the North's nuclear stance, noting China's "special relationship" with Pyongyang.

Earlier Tuesday, South Korea's Finance Ministry said it has imposed sanctions on three North Korean companies for helping the country's controversial April 5 long-range rocket test. The move was largely symbolic because the firms don't do business with South Korea.

The North's recent saber rattling has come amid reports that the regime's absolute leader, Kim Jong Il, has reportedly tapped his third and youngest son -- Jong Un -- as his successor.

In an interview aired Tuesday in Tokyo, a man believed to be Kim's eldest son -- Jong Nam -- said he believes recent media reports that say his youngest brother will become the communist country's next leader.

"My father loves very much my brother as his son. I hope he can do his best for North Korean people for their happiness and better life," the man said in an interview with Japanese broadcaster TV Asahi in Macau.

Who will become the North's next leader has been the focus of keen media attention as the 67-year-old Kim Jong Il reportedly suffered a stroke and underwent brain surgery last summer.

Yonhap, meanwhile, reported Tuesday that South Korea had doubled the number of naval ships around the disputed sea border with the North amid concern the communist neighbour could provoke an armed clash there -- the scene of skirmishes in 1999 and 2002.

The Joint Chiefs of Staff declined to confirm the report, but said the North has not shown any unusual military moves.

Relations between the two Koreas have significantly worsened since a pro-U.S, conservative government took office in Seoul last year, advocating a tougher policy on the North. Since then, reconciliation talks have been cut off and all key joint projects except the factory park in Kaesong have been suspended.

Some 40,000 North Koreans are employed at the zone, making everything from electronics and watches to shoes and utensils, providing a major source of revenue for the cash-strapped North. The park combines South Korean technology and management expertise with cheap North Korean labour.

A total of 106 South Korean companies operate in the park. That number will go down by the end of the month when Skinnet, the fur-maker, completes its pullout.

A Skinnet company official said the decision was primarily over "security concerns" for its employees, and also because of a decline in orders from clients concerned over possible disruptions to operations amid the soaring tensions.

The official spoke on condition of anonymity because he was not authorized to speak with reporters.

The industrial park's fate has been in doubt since last month when North Korea threatened to scrap all contracts on running the joint complex and said it would write new rules of its own and the South must accept them or pull out of the zone.

The companies have also been concerned by the detention of a South Korean man working at the complex by North Korean authorities since late March for allegedly denouncing the regime's political system.

The two sides are to hold talks on the fate of the park Thursday.

Intensifying its confrontation with the U.S., North Korea handed down 12-year prison terms to two detained American journalists on Monday.