Four Japanese politicians made a short visit on Tuesday to a group of disputed islands in the East China Sea, prompting an official protest from Beijing.

Japanese officials say four municipal politicians from Okinawa visited the rocky, uninhabited chain of islands, known as Senkaku in Japan and Diaoyu in China.

The strategic and energy-rich islands are controlled by Japan, but also claimed by China and Taiwan.

Such visits are regularly interpreted by China as a violation of its sovereignty. The Chinese Foreign Ministry said Tuesday the islands have been part of China since ancient times, vowing to protect what it sees as its territory in the region.

Meanwhile, a group of 10 activists from Hong Kong, Taiwan and China are reported to be en route to the disputed islands.

The squabble comes days after Japanese Prime Minister Yoshihiko Noda visited Beijing, where he agreed to hold high-level meetings in order to help reduce maritime tensions.

Relations between China and Japan sank to the lowest point in years after Japan arrested the captain of a Chinese fishing boat that collided with a Japanese coast guard vessel in the East China Sea in September 2010.