Regional tempers flared in Asia on Wednesday — the anniversary of the end of World War II combat — after Japan arrested more than a dozen Chinese activists who had landed on part of a disputed island chain in the East China Sea.

The conflict is the latest in a string of blowups over the disputed island territories, and it exacerbated tensions on the anniversary of the Japanese surrender in 1945, a date that still stirs bad blood among Japan’s neighbors because of its brutal wartime occupation of large swaths of East Asia.

Shortly after the activists’ arrest, China vowed to lodge a formal complaint with Japan.

The activists had set out from Hong Kong for the islands, which are called Diaoyu by the Chinese and Senkaku by Japan. They carried with them five Chinese flags, reportedly intending to evade Japanese authorities patrolling the islands and to use the flags to claim the territory for China.

Many Chinese activists have embarked on similar forays in recent years, and several have been turned away by Japanese authorities.

According to the group behind Wednesday’s attempt, the party encountered setbacks along the way, including problems with weather and lost food supplies before finally nearing the islands Wednesday afternoon.

The group’s representative said the activists evaded several Japanese coast guard boats, which tried to pummel them with water cannons.

Japanese authorities said they arrested five of the activists after they swam ashore.

A spokesman for China’s Foreign Ministry issued a statement urging Japan to refrain from doing anything that would endanger Chinese citizens or their property.

In a separate protest Wednesday, a group of South Koreans, who harbor a similar grudge stemming from the war, swam to a different set of islands in dispute between South Korea and Japan. That incident, however, centered on a 137-mile relay swim that was led by a South Korean pop singer.

The swim followed a controversial first-ever visit last week to the islands by a South Korean president, an event that prompted Japan to lodge a formal complaint of its own with South Korea and order its senior diplomat to return from Seoul.

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A map locating Senkaku Islands (By Laris Karklis/The Washington Post)

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