In an unexpected meeting on the sidelines of the G-20 summit, the Chinese and Japanese leaders shook hands and spoke to each other. China's Xi Jinping and Japan's Shinzo Abe have not met since the Chinese leader took power in March 2013 and the the Japanese leader in December 2012. Ties between the two sides have been severely strained by a territorial dispute. Both sides claim islands in the East China Sea. The islands, known as Senkaku in Japan and Diaoyu in China, are controlled by Japan. But China was angered last year when the Japanese government bought three of the islands from their private Japanese owner. Since then, Chinese government vessels have been sailing in and out of what Japan says are its territorial waters around the islands.