Three Chinese ships entered what Japan considers its territorial waters near disputed islands in the East China Sea on Monday, Sept 24, the Japanese government said, prompting an official protest and renewed diplomatic efforts to cool tensions, Reuters reported.

The move comes a day after China called off celebrations to mark the 40th anniversary of the normalization of ties between the Asia's largest economies and as officials from China's ruling Communist Party, due to arrive in Tokyo on Monday, canceled their trip.

China's Xinhua news agency said two civilian surveillance ships were undertaking a "rights defense" patrol near the islands, citing the State Oceanic Administration, which controls the ships. One fishery patrol vessel was also detected inside waters claimed by Japan, the Japanese Coast Guard said.

Japan said it had lodged an official protest.

Sino-Japanese relations deteriorated sharply after Japan bought the islands, called Senkaku in Japan and Diaoyu in China, earlier this month, sparking anti-Japan protests in cities across China.