The Chinese ambassador to Japan on Tuesday rebuffed Tokyo's protests over the presence of Chinese ships around the Diaoyu Islands.

It is "natural" for them to operate in Chinese territory, ambassador Cheng Yonghua said after being summoned by Japan's Foreign Minister Fumio Kishida on Tuesday morning. Kishida lodged a protest over the increased number of Chinese vessels in waters around the Diaoyu Islands.

According to Japanese media, Japan has lodged at least six protests with China through various channels since Friday, on issues ranging from Chinese ships to an infrared camera on a Chinese oil and gas field exploration platform in the East China Sea.

It was reported that Cheng was also summoned on Friday by Japanese Vice-Foreign Minister Shinsuke Sugiyama after six Chinese coast guard vessels and six fishing vessels entered the waters.

Kyodo reported that Kishida told Cheng that China-Japan relations are "deteriorating badly". Cheng responded that it is normal for China's vessels to sail in its own territory.

The move comes as the number of Chinese coastguard ships around the Diaoyu Islands rose to as many as 13 on Tuesday, according to the Japanese coast guard - a record number since China started sending ships to the region in September 2012 after Japan "nationalized" the islands.

According to The Associated Press, Cheng told reporters as he left the ministry that the increase in China's fleet was to oversee the increased activity of Chinese fishing boats. The fishing season in the East China Sea has opened.

"Please understand that it's an effort by the Chinese side to avoid further complications in the situation," Cheng said.

Yu Zhirong, a maritime studies researcher at the China Maritime Development Research Center, said that because of disturbances from Japan, Chinese fishermen were forced several years ago to stop fishing in waters around the Diaoyu Islands, a traditional Chinese fishing ground.

"Now we are asserting our sovereignty rights. The protests made by Japan are unreasonable and null," Yu said.

Huang Dahui, a researcher on East Asia studies at Renmin University of China, said repeated protests by the Japanese side are driven by hidden political motives, including Japanese Prime Minister Shinzo Abe's efforts to amend his country's Constitution.

Japanese media reports say the recent escalation in China's activity may be seen as a warning against planned visits by members of Prime Minister Shinzo Abe's Cabinet to Tokyo's Yasukuni Shrine, which honors war dead including a number of war criminals, on the Aug 15 anniversary marking the end of World War II.

Also on Tuesday, Beijing said Tokyo is making a fuss by hyping a normal infrared camera installed on an oil and gas field exploration platform.

The remarks, made by the spokesperson's office of the Foreign Ministry, came after Japanese media said the Japanese government believes the move could help China improve its military capability in the East China Sea.

According to the office, the equipment the Japanese side mentioned is a normal infrared camera, and its aim is to observe the situation around the platform and ensure its security.

Zhang Yaozhong contributed to this story.

lixiaokun@chinadaily.com.cn

(China Daily 08/10/2016 page8)