A Pandora's box in terms of diplomatic relations between Tokyo and Seoul may have just been opened with South Korea's top court upholding a lower court ruling Tuesday that Nippon Steel & Sumitomo Metal Corp. should pay about ¥40 million in compensation to four Koreans forced to work in Japan during World War II.

The Japanese government, as would be expected, immediately reacted strongly to the ruling, with Foreign Minister Taro Kono saying "the primary legal basis of the bilateral relations between the two countries has been fundamentally undermined."

The court ruling came despite admissions by all past South Korean administrations that the issue of labor compensation involving Japan's colonial rule of the peninsula had been resolved by a 1965 pact between Tokyo and Seoul.