President Donald Trump announced Wednesday that he has ordered the Department of Defense to begin testing U.S. nuclear weapons “immediately” in response to nuclear tests conducted by rival countries.

This announcement came moments before his scheduled meeting with Chinese President Xi Jinping.

Trump claimed in a social media post that the United States “has more nuclear weapons than any other country,” mentioning Russia in second place and China “in a distant third, but that they will be tied within five years.”

“Because of other countries’ testing programs, I have ordered the War Department to begin testing our nuclear weapons on a level playing field. That process will begin immediately,” Trump declared.

Trump’s post on Truth Social included very few details about what the tests would entail.

The last U.S. nuclear weapons test was conducted in 1992, before former President George H.W. Bush implemented a moratorium on nuclear weapons testing.

These tests were conducted at the end of the Cold War.

This is a radical change in US policy, because “a voluntary moratorium on nuclear explosives testing has been maintained since 1992,” according to the Library of Congress.

Trump made the announcement from South Korea, hours after Russian President Vladimir Putin said that Moscow had successfully tested a nuclear-capable underwater drone called Poseidon and, days earlier, a nuclear-powered cruise missile named Burevestnik.

President Donald Trump and Chinese leader Xi Jinping have arrived in Busan, South Korea, where they will discuss a trade deal between the world's two largest economies.

Trump's decision to include nuclear power in the discussion comes just before he begins his meeting with his Chinese counterpart, Xi Jinping, for a high-level trade summit.