FILE PHOTO: The Pentagon is seen from the air in Washington, D.C., U.S., March 3, 2022. REUTERS/Joshua Roberts/File Photo
U.S. Defense Secretary Pete Hegseth speaks during a joint press conference with Japan's Defense Minister Shinjiro Koizumi (not pictured), in Tokyo, Japan, Oct. 29, 2025. Eugene Hoshiko/Pool via REUTERS
U.S. President Donald Trump speaks during a meeting with South Korean President Lee Jae Myung (not pictured) on the sidelines of the Asia-Pacific Economic Cooperation (APEC) leaders' summit in Gyeongju, South Korea, October 29, 2025. REUTERS/Evelyn Hockstein

By Trevor Hunnicutt, Ismail Shakil and Kanishka Singh

BUSAN, South Korea (Reuters) -U.S. President Donald Trump on Thursday ordered the U.S. military to immediately resume testing nuclear weapons for the first time in 33 years, minutes before beginning a high-stakes meeting with Chinese President Xi Jinping.

Trump made the surprise announcement on Truth Social while he was aboard his Marine One helicopter flying to meet Xi for a trade negotiating session in Busan, South Korea. He said he was instructing the Pentagon to test the U.S. nuclear arsenal on an "equal basis" with other nuclear powers.

"Because of other countries testing programs, I have instructed the Department of War to start testing our Nuclear Weapons on an equal basis. That process will begin immediately," Trump posted.

"Russia is second, and China is a distant third, but will be even within 5 years."

He did not elaborate and did not reply to a reporter's shouted question about his post after his initial remarks to Xi. It was not immediately clear whether Trump was referring to nuclear-explosive testing, which would be carried out by the National Nuclear Safety Administration, or flight testing of nuclear-capable missiles.

CHINA MORE THAN DOUBLED NUCLEAR ARSENAL IN LAST 5 YEARSTrump's decision to restart nuclear weapons testing follows a rapid expansion by China of its nuclear stockpile in recent years, and came just after Russia announced what it called a successful test of a nuclear-powered and nuclear-capable cruise missile as well as a nuclear-powered torpedo.

Trump addressed the Russian moves aboard Air Force One earlier this week, telling reporters that Russian President Vladimir Putin should be working to end the war in Ukraine "instead of testing missiles."

Beijing has more than doubled the size of its arsenal to an estimated 600 nuclear weapons in 2025 from 300 weapons in 2020, according to the Center for Strategic and International Studies, a Washington-based think tank.

It said U.S. military officials estimate that China will have over 1,000 nuclear weapons by 2030. A Victory Day parade in September revealed five nuclear capabilities that can all reach the continental United States, CSIS said.

Putin said on Wednesday Russia had successfully tested a Poseidon nuclear-powered super torpedo that military analysts say is capable of devastating coastal regions by triggering vast radioactive ocean swells.

As Trump has toughened both his rhetoric and his stance on Russia, Putin has publicly flexed his nuclear muscles with the test of a new Burevestnik cruise missile on October 21 and nuclear launch drills on October 22.

In August, Trump said he had discussed nuclear arms control with Putin and wanted China to get involved. Beijing responded by saying it was "unreasonable and unrealistic" to ask the country to join in nuclear disarmament negotiations with the two countries, since its arsenal was much smaller.

Trump had first laid out his intention to pursue nuclear arms control efforts in February, saying he wanted to begin discussions with both Putin and Xi about imposing limits on their arsenals.

The United States last tested a nuclear weapon in 1992.

Tests provide evidence of what any new nuclear weapon will do - and whether older weapons still work.

Apart from providing technical data, such a test would be seen in Russia and China as a deliberate assertion of U.S. strategic power.

The United States opened the nuclear era in July 1945 with the test of a 20-kiloton atomic bomb at Alamogordo, New Mexico, and then dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki in August 1945 to end World War Two.

(Reporting by Trevor Hunnicutt, Ismail Shakil, Kanishka Singh and Andrea Shalal; Editing by Donna Bryson, Lincoln Feast and Stephen Coates)