Japan lodged a protest with China on Friday after four Chinese state-owned ships entered Japanese territorial waters around a chain of disputed islands in the East China Sea. The Foreign Ministry conveyed the protest to the Chinese Embassy in Tokyo over the intrusion and demanded the vessels leave Japanese waters immediately. "The Senkaku islands are inherently Japanese territory in light of history and international law," the ministry said. The Japan Coast Guard said it spotted four Chinese Coast Guard vessels in the morning in sovereign waters off the Japan-administered Senkaku Islands, which are also claimed by China and Taiwan. The coast guard warned the Chinese ships via radio to leave the waters immediately. The vessels left after three hours, according to the coast guard. A Cabinet task force met at Prime Minister Shingo Abe's Office to gather information and monitor the situation. The small chain of uninhabited rocky islands, known as Diaoyu in China and Tiaoyutai in Taiwan, lie in rich fishing grounds and waters thought to contain large deposits of oil and natural gas. Relations between the world's second and third-largest economies have sharply deteriorated since Tokyo's nationalization of three of the five major islands in September 2012 through purchase from a private Japanese owner.