Japan's Prime Minister Shinzo Abe says it is "extremely regrettable" that a Chinese warship locked its pre-firing radar on a Japanese navy boat near disputed islands last week.
Speaking to a parliamentary session Wednesday, Abe called the move "dangerous." He said it could lead to an accidental clash, and he warned China against escalating the situation further.
"At a time when it seemed there are signs of improvement towards increasing talks between Japan and China, having this sort of one-sided provocative action taken by the Chinese is extremely regrettable," said Abe.
Tokyo has lodged an official protest with Beijing over the January 30 incident, the latest in a series of dangerous escalations in their long-running dispute over ownership of a group of East China Sea islands.
On Tuesday, Japan's defense ministry said it confirmed that the Chinese navy frigate aimed its weapons-targeting radar at the Japanese vessel. It also said a Japanese military helicopter was targeted with similar radar earlier last month.
Since late last year, China has regularly sent government ships to patrol the Japanese-administered islands, in what observers say is an effort to establish de facto control of the area. Both sides also have scrambled fighter jets to the islands, raising fears of an all-out military conflict.
China-Japan ties sank to their lowest level in years last September, after Tokyo purchased some of the islands from their private Japanese landowner. The move sparked days of angry protests in China. It also damaged trade ties between Asia's two largest economies.
The situation has remained tense, with government ships from both sides regularly exchanging warnings in the disputed waters. But both sides have hinted in recent days that diplomacy, and not military conflict, is the best way to resolve the issue.
Prime Minister Abe, who is known for his hawkish and nationalistic views, last month said he would consider a summit with China to help ease tensions surrounding the island dispute. Senior Chinese officials welcomed the offer, although no meeting has been planned.
The uninhabited islands, known as Senkaku in Japan and Diaoyu in China, are surrounded by rich fishing grounds and possibly by energy deposits. They have a long history of causing tensions between China and Japan.
Japan annexed the islets in the late 19th century. China claimed sovereignty over the archipelago in 1971, saying ancient maps show it has been Chinese territory for centuries.