Defense Secretary James Mattis reassured Japan over the weekend that the United States would defend a pair of disputed islands in the East China Sea controlled by Tokyo but also claimed by Beijing.
Mattis, who was conducting his first overseas trip under the Trump administration to East Asia, told Japanese officials on Saturday that the U.S. commitment to defend the country extended to the uninhabited Senkaku Islands, known in China as the Diaoyus, the New York Times reported.
Speaking at a news conference in Tokyo, Mattis cited Article 5 of the U.S.-Japan Security Treaty, which pledges American defense of Japanese territories.
"I want there to be no misunderstanding during the transition in Washington that we stand firmly, 100 percent shoulder-to-shoulder with you and the Japanese people," Mattis said.
Tensions over the rocky outposts have escalated in recent years with Japanese and Chinese ships regularly operating nearby as Beijing attempts to counter Tokyo’s control.
Chinese Foreign Ministry spokesman Lu Kang condemned America’s defense of the islands, accusing Mattis of perpetuating instability in the region.
"Diaoyu and its affiliated islands have been Chinese territory since ancient times. These are historical facts that cannot be changed," Lu said in a statement. "The so-called US-Japan security treaty was a product of the Cold War, and it should not harm China's territorial sovereignty and legitimate rights."
"We urge the U.S. side to adopt a responsible attitude and stop making wrong remarks on the issue of the sovereignty of Diaoyu Islands," Lu added.
Prior to his arrival in Japan, Mattis traveled to South Korea on Thursday to reassure its longtime Pacific ally. He pledged to talk to Seoul officials about the deployment of a missile defense system intended to combat North Korean aggression.
Mattis said he would use his trip to East Asia to gauge the opinions of leaders in Seoul and Tokyo on how to best confront Pyongyang.
"Two of the most enduring alliances that we have had have been between Japan and us, and of course South Korea and the United States, and together we confront the North Korean situation," Mattis told reporters last week.