The defense chiefs of Japan and the United States on Saturday confirmed that the Senkaku Islands in the East China Sea fall under the scope of a security treaty between the two countries.

Speaking by phone, both Defense Minister Nobuo Kishi and U.S. acting Defense Secretary Christopher Miller referred to the application of Article 5 of the treaty to contingencies surrounding the Japan-controlled, China-claimed islands, according to the Defense Ministry.

The article obligates the United States to respond to armed attacks on territories under Japan's administration. Separately, U.S. President-elect Joe Biden on Thursday assured Prime Minister Yoshihide Suga in their first phone talks that Washington will help defend the uninhabited islands.

"We are opposed to a unilateral change of the status quo" by force, Kishi was quoted by the ministry as saying on China's rising maritime assertiveness during his conversation with Miller, who assumed the post after U.S. President Donald Trump's announcement on Monday that he had fired Defense Secretary Mark Esper.

China, which has stepped up its territorial claims in the East and South China seas, regularly sends ships to waters near the Senkaku Islands, which it calls Diaoyu.

Other issues discussed by Kishi and Miller included North Korea and Japan's new missile defense plan, according to the ministry.

They agreed that Japan and the United States will continue to cooperate in cracking down on North Korea's ship-to-ship transfers of goods banned by the U.N. Security Council, in addition to sharing concern over Pyongyang's missile development program, it said.