TOKYO — Japan’s defense minister, Satoshi Morimoto, said Friday that he wanted to revise his nation’s security alliance with the United States to place more emphasis on the threat from China to islands at the center of a territorial dispute.

Mr. Morimoto said he wanted to update a set of guidelines that govern how the two allies’ militaries would cooperate during a crisis to include the potential for a maritime clash with China. Tensions between Japan and China have risen in recent months over the contested islands in the East China Sea known as the Senkaku in Japan and Diaoyu in China.

In a sign of the emotions conjured by the territorial dispute, China has kept up the pressure on Japan by sending paramilitary ships into waters around the islands, which are controlled by the Japanese but also claimed by China and Taiwan. On Friday, Japan’s Coast Guard said Chinese surveillance ships had sailed into Japanese-claimed waters near the islands for the 21st consecutive day.

Mr. Morimoto did not specify exactly what changes he would seek in the agreement. He told reporters that he had already informed the United States of Japan’s desire to revisit the guidelines, and on Friday he sent the vice minister of defense, Akihisa Nagashima, to Washington for talks.