Japan and China have been involved in a series of incidents in recent months in the East China Sea where Chinese and Japanese naval vessels regularly shadow each others movements.

Both countries claim a small clusters of islands, known as Diaoyu in China and Senkaku in Japan, believed to be rich in oil and gas. Controlled by Japan, possession of the uninhabited outcrops and the sea surrounding them would provide China with easier access to the Pacific.

Hopes had been rising for an easing in tensions, including a possible summit between Japanese Prime Minister Shinzo Abe and Chinese leader Xi Jinping. But the radar issue has seen China and Japan engage in a fresh round of invective.

China’s Defence Ministry on Thursday said Japan’s complaints did not “match the facts”. The Chinese ship’s radar, it said, had maintained regular alerting operations and the ship “did not use fire control radar”.

Japan’s position against China has hardened since Abe led his conservative party to a landslide election victory in December, promising to beef up the military and stand tough in territorial disputes.

The commander of US forces in the Asia-Pacific said the squabble between Japan and China underlined the need for rules to prevent such incidents turning into serious conflict.

China also has ongoing territorial disputes with other Asian nations including Vietnam and the Philippines over islands in the South China Sea.