The Chinese Premier Wen Jiabao has threatened further action against Japan unless it frees the Chinese boat captain arrested in disputed water earlier this month. In his first comment in the dispute, Mr. Wen demanded his immediate and unconditional release. The dispute erupted when a Chinese fishing trawler and two Japanese coast guard vessels collided on September 7 near disputed islands that lie in rich fishing grounds and near possible oil and gas fields. Japan arrested the 41-year-old captain Zhan Qixiong the following day, citing its domestic law. On Sunday, a court extended his detention until September 29, when he must be either indicted or released.