On June 30, 2008, the leading official of the Asian Department of the Foreign Ministry summoned officials of the Japanese Embassy in Beijing and protested at the Japanese government's tolerating the so-called "aerial inspection" by several Japanese Diet members, disregarding China's strong opposition. The official stressed the Diaoyu Islands had been Chinese territory since ancient times and China held indisputable sovereignty over the islands. The official demanded the Japanese side stop activities infringing China's sovereignty so as to prevent such incidents happening again.