BEIJING, April 21 -- China's seizure of a Japanese ship was solely for delayed rent and losses owed to a Chinese firm and was unrelated to wartime compensation, Foreign Ministry spokesman Qin Gang said on Monday.

His comments came after Japan's chief government spokesman, Yoshihide Suga said the seizure undermined the 1972 joint communique that normalized ties between Japan and China, in which Beijing agreed to renounce "its demand for war reparation from Japan."

Shanghai Maritime Court detained a Japanese ship, Baosteel Emotion, owned by Mitsui O.S.K. Lines (MOL) on Saturday, to pay delayed rent and losses to a Chinese firm.

The Japanese shipping firm was sued in 1988 over alleged delays in rent payments for two ships and economic losses dating back to the 1930s. The maritime court ruled in 2007 that it should compensate the Chinese firm 2.9 billion Japanese Yen (28.4 million U.S. dollars). Shanghai Municipal Higher People's Court made a final verdict in 2010, defending the 2007 judgement.

The court said it will dispose of the ship if MOL continues to refuse to fulfill its obligation.

"As a commercial lawsuit, the enforcement of the verdict was carried out at the request of the plaintiff. It is unrelated to wartime compensation," Qin said.

China's stance to uphold the joint communique signed in 1972 remains unchanged, Qin said.

He reiterated China would continue to protect the legitimate rights of foreign businesses operating in the country.