China’s attempt to challenge Japan’s control of islands in the East China Sea by sending patrol ships to nearby waters was planned since 2006, much earlier than had previously been believed by the Japanese government, a former commanding officer of the China coast guard has said.

A Chinese coast guard vessel first entered Japanese territorial waters around the Senkaku Islands, which China calls Diaoyu, in December 2008. The Japanese government has since assumed that the commander of the vessel acted on his own initiative.

But according to Yu Zhirong, an officer on the vessel when it entered Japanese waters on Dec. 8, 2008, an order came directly from the central government based on a plan devised in 2006 to regularly send patrol ships to the area.

China decided to step up its maritime activity around the Senkakus after a Japanese patrol vessel and a Taiwanese ship collided near one of the uninhabited islets in June 2008, Yu told Kyodo News.

Taiwan also claims the islands, which it calls Tiaoyutai.

Then, as tensions between the countries grew following the collision of a Japan Coast Guard ship and a Chinese trawler in September 2010, China began sending patrol vessels to the Japanese territorial waters more frequently.

Tensions continued to escalate after Tokyo brought the Senkakus under state control in September 2012, which prompted the most prominent flare-up of Chinese public anger toward Japan seen in years.