STORY HIGHLIGHTS

Hong Kong (CNN) -- The fragile relationship between China and Japan came under fresh strain Tuesday as ships from both sides crowded into the waters around a disputed group of islands and nearly 170 Japanese lawmakers visited a controversial war memorial.

The Japanese Coast Guard said eight Chinese government ships had entered waters near the contested islands in the East China Sea on Tuesday morning, the largest number to do so at any one time since tensions surrounding the territorial dispute escalated last year. China said its ships were there to monitor the movements of Japanese vessels in the area after a Japanese nationalist group chartered a flotilla of fishing boats to take dozens of activists there.

The Japanese foreign ministry responded by summoning the Chinese ambassador in Tokyo to lodge a strong protest about the Chinese ships' presence near the uninhabited islands that lie between Okinawa and Taiwan and are known as Senkaku in Japanese and Diaoyu in Chinese.

A day earlier, Beijing had made its own protest to Tokyo about a visit at the weekend by three Japanese cabinet ministers to the Yasukuni Shrine in Tokyo, which honors Japanese people killed while fighting for their country, including convicted war criminals.

Countries that suffered heavily at the hands of the Japanese military before and during World War II, such as China and South Korea, consider the shrine as an emblem of that aggressive period in Japanese history.

But China's representations failed to deter 168 Japanese members of parliament from visiting the shrine on Tuesday to pay their respects to the war dead, the most to do so in recent years.

New men in charge

New leaders have taken office in both countries in the past few months: Prime Minister Shinzo Abe in Japan and President Xi Jinping in China. They inherited a highly delicate situation concerning the disputed islands that analysts have warned could spiral out of control -- a concern for the United States, which has a mutual security treaty with Japan.

"Despite expressions by both governments that they wish to avoid a war, potential for escalation has increased and there is deepening pessimism on both sides over the prospects of a peaceful settlement," the International Crisis Group said in a report this month on the tensions between Japan and China.

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China, Japan face off over islands