Tensions escalated once again between Japan and its neighbors on Tuesday as China strongly protested against "provocation" by Japanese ships in the waters off the Diaoyu Islands, calling the moves "illegal" and "troublemaking".

A group of 168 Japanese lawmakers visited the controversial Yasukuni Shrine in Tokyo on the same day, despite repeated objections from Beijing and Seoul. The visit worsened Japan's diplomatic deadlock in the region.

According to a statement issued by China's State Oceanic Administration, a fleet of Chinese marine surveillance ships on regular patrol duty found several Japanese ships in waters around the Diaoyu Islands on Tuesday.

"Organized in four formations, the eight Chinese ships monitored the Japanese ships ... and by 10 am, the Japanese vessels had left the Diaoyu waters under China's law enforcement pressure," the statement said.

Ten boats carrying about 80 Japanese activists entered the waters off the Diaoyu Islands, claiming to be conducting fishery studies, Japanese media reported.

China strongly protested and has lodged solemn representations to Japan regarding Japanese "right-wingers' illegal entry" into the waters, Foreign Ministry spokeswoman Hua Chunying said at Tuesday's news conference.

Zhou Yongsheng, an expert on Japanese studies at China Foreign Affairs University, said China should fight back against any challenges from Japanese right-wingers in order to protect its sovereignty and territorial integrity.

"It's great to see that China's SOA has successfully performed its function of safeguarding territorial rights since its restructuring in March," Zhou said.

Shrine visit

Ties between Beijing and Tokyo have been strained since last September when Japan attempted to "nationalize" the islands. Recently, they have been further haunted by historical issues.

The Yasukuni Shrine visit by Japanese lawmakers marked the first time the number of lawmakers visiting the shrine has exceeded 100 since October 2005, according to Xinhua News Agency.

Japanese senior Vice-Minister of Finance Shunichi Yamaguchi, Senior Vice-Minister of Environment Shinji Inoue and policy chief of the ruling Liberal Democratic Party Sanae Takaichi were among the visitors.

Their visit followed Abe's ritual offering of a pine tree and three cabinet ministers' weekend visits to the shrine, which honors convicted war criminals during World War II.

Hua, the spokeswoman, said Japanese political leaders should stop taking such actions, which only serve to isolate Tokyo from the international community.

"Regardless of what method or what identity these Japanese leaders assume when they visit the shrine, its nature is to deny Japan's past militaristic aggression," Hua said.

"We urge Japan to be responsible to history, to the people and to the future, and take realistic measures to win the trust of the international community, and stop causing harm to itself and others," she added.

South Korea is also strongly against Japanese leaders' visits to the controversial shrine.

Cho Tai-young, a South Korean government spokesman, expressed deep concern and regret over the visits, calling the shrine "a place to glorify Japan's aggressive war".

A day earlier, South Korean Foreign Minister Yun Byung-se called off a planned visit to Tokyo, Yonhap News Agency reported.

Xinhua contributed to this story.