TOKYO — Japan said Tuesday that a Chinese military vessel trained a radar used to help direct weapons last week on a Japanese naval vessel near disputed islands in the East China Sea. The Japanese Defense Ministry also said that a Chinese frigate directed the same kind of radar at one of Japan’s military helicopters in a previously undisclosed episode on Jan. 19.

In both cases, the Japanese government said, the Chinese ships eventually turned off the radar without firing, but the defense minister, Itsunori Onodera, warned that such actions increased the chances that any missteps in a dispute over the islands could veer into a larger confrontation.

The Chinese Ministry of Defense did not answer calls regarding Japan’s claims about the use of the radar, and China’s Ministry of Foreign Affairs had no immediate comment.

Mr. Onodera said that in the latest episode, a Chinese Navy frigate directed its fire-control radar at a Japanese destroyer on Jan. 30 near the islands known as the Senkaku in Japan and the Diaoyu in China that are controlled by Japan but also claimed by China and Taiwan.