SEOUL (REUTERS) - South Korean plaintiffs in a World War II forced labour court case against Japan's Nippon Steel & Sumitomo Metal Corp have applied to seize some of Nippon Steel's Korean assets, a South Korean newspaper reported on Wednesday (Jan 2).

The application for the asset seizure, if approved by the court in Seoul, could further strain what are already frosty bilateral relations between Japan and South Korea over the issue.

It stems from a ruling by South Korea's Supreme Court in October that Nippon Steel must pay compensation of 100 million won (S$122,000) to each of four South Koreans for forced labour during the war.

The Japanese government has denounced the verdict, saying all wartime reparations were dealt with in a 1965 treaty that normalised ties between the two East Asian nations.

The South Korean plaintiffs recently applied to the court for the seizure of Nippon Steel's shares in a Korea-based joint venture with steelmaker Posco called "Posco-Nippon Steel RHF Joint Venture", according to the Chosun Ilbo newspaper.

Nippon Steel owns a 30 per cent stake, or 2.34 million shares, of the joint venture, worth about 11 billion won, it reported. The paper did not say how much the Korean plaintiffs sought from the seizure.

Lawyers representing the South Korean plaintiffs did not respond immediately to a request for comment. Representatives for courts with jurisdiction over the joint venture's South Korean offices could not be reached immediately for comment.

Repeated calls to Nippon Steel's office went unanswered. Wednesday is a holiday for most businesses in Japan.

Nippon Steel called it "extremely regrettable" at the time of the ruling but said it would review the decision carefully in considering further steps.

Posco declined to comment.