SINGAPORE — A bitter sea dispute between China and Japan, Asia's two biggest economies, is intensifying after the decision of a Japanese court Sunday to extend detention of a Chinese fishing boat captain until Sept. 29.

As state television in Beijing reported that China had suspended ministerial exchanges with Japan and halted talks on increasing flights, a Chinese foreign ministry spokesman warned that "strong reactionary measures" would be taken unless Japan released the captain without conditions.

Tokyo last week returned the Chinese crew and fishing boat it accuses of operating illegally near the Japanese- administered Senkaku Islands in the East China Sea and ramming two Japanese Coast Guard vessels while trying to escape. Beijing says the islands belong to China and has demanded the immediate return of the trawler's captain. However, even if Japan complies, the underlying territorial and maritime boundary conflict with China remains unresolved.