In a dramatic move that has sent shockwaves through global diplomatic and defense circles, former U.S. President Donald Trump on Thursday ordered the immediate resumption of American nuclear weapons testing after a 33-year hiatus. The announcement came just minutes before his scheduled meeting with Chinese President Xi Jinping in Busan, South Korea.

Trump made the surprise declaration on Truth Social while en route to the meeting aboard Marine One, stating that the Pentagon would begin testing 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.”

The post appeared to be a pointed message to both Xi, whose government has significantly expanded China’s nuclear stockpile in recent years and to Russian President Vladimir Putin, amid heightened tensions over recent Russian weapons trials.