Former U.S. Assistant Secretary of State for East Asian and Pacific Affairs Kurt Campbell says Washington warned Japan against purchasing and nationalizing the Senkaku islands last fall.

Campbell told Japan’s Kyodo News that the U.S. State Department offered Tokyo strong advice not to go in that direction regarding the islands, known as Senkaku in Japanese and Diaoyu in Chinese.

Campbell said the government stressed the purchase could “trigger a crisis” with China, which claims the islands for itself.