Two Chinese marine surveillance ships have entered what Japan considers to be its territorial waters near disputed islands in the East China Sea, the Japanese Coast Guard says.
China's Xinhua news agency confirmed that two civilian surveillance ships were undertaking a "rights defence" patrol in waters near the disputed islands on Monday. The news agency cited the State Oceanic Administration, which controls the ships.
As of 7:00am local time (22:00 GMT) on Sunday, two Chinese maritime surveillance ships were spotted in waters off Kubashima and Uotsurijima, the Japanese Coast Guard said.
Sino-Japanese relations deteriorated sharply after Japan bought the islands, called Senkaku in Japan and Diaoyu in China, sparking anti-Japan protests in cities across China.
"In recent days, Japan has constantly provoked incidents concerning the Diaoyu islands issue, gravely violating China's territorial sovereignty," China's Xinhua news agency said.
The ship patrols were intended to exercise China's "administrative jurisdiction" over the islands, it said.
"Following the relevant laws of the People's Republic of China, [the ships] again carried out a regular rights defence patrol in our territorial waters around the Diaoyu islands."
Al Jazeera's Steve Chao, reporting from the islands says: "The fishermen say they have seen a number of Chinese ships, who they say are playing a dangerous game of cold war cat and mouse games".
"Chinese media says they are aware of the ships, but states the ships are on patrol in China's administrative area," says our reporter.
The Japanese Coast Guard ordered the Chinese ships to move out of the area, but received no response, an official said.
Sino-Japanese ties have long been plagued by China's memories of Japan's military aggression in the 1930s and 1940s and present rivalry over regional influence and resources.
The islets are located near rich fishing grounds and potentially huge gas reserves.