Japan lodged a formal protest with the Chinese government on Tuesday after it said a Chinese warship directed a radar used to aim missiles at a Japanese warship, in a new escalation of a standoff over disputed islands.

The Japanese defense minister, Itsunori Onodera, said that a Chinese navy frigate had directed its fire-control radar at a Japanese destroyer in the incident on Jan. 30 near the islands in the East China Sea, known as the Senkaku in Japan and Diaoyu in Chinese. The uninhabited island group has been controlled by Japan for decades, but claimed by China and also Taiwan.

On Tuesday, the Defense Ministry also disclosed that a Chinese frigate had directed the same kind of radar at a Japanese military helicopter in a previously undisclosed incident on Jan. 19. In both cases, the Chinese ships eventually turned off the radar without actually firing a shot.

More: Japan Says China Aimed Weapons-Targeting Radar at Ship