Beijing ? Japan said today it was not officially informed of China’s decision to break off high-level government contacts over the extended detention of a fishing boat captain arrested after a ship collision near disputed islands.

The rare move pushed already tense relations to a new low, and showed China’s willingness to play hardball with its Asian rival on issues of territorial integrity.

The decision late Sunday came a day after anti-Japanese protests were held across China on the anniversary of the start of a Japanese invasion of China in 1931 that has historically cast a shadow over ties between the world’s second- and third-largest economies.

The latest spat between Tokyo and Beijing was sparked when the Chinese vessel collided with two Japanese coast guard ships on Sept. 7 near islands in the East China Sea claimed by both countries. The 14 Chinese crew were released last week, but the captain’s detention for further questioning — pending a decision about whether to press charges — has inflamed ever-present anti-Japanese sentiment in China.