President Donald Trump says he has instructed the Pentagon to immediately start testing nuclear weapons, citing a need to match “other countries [sic] testing programs.”

Trump’s post on Truth Social included very few details on the nature of the tests, but says the “process will begin immediately.” It’s not clear whether Trump is referring to explosive tests of nuclear warheads or tests of systems capable of delivering them.

The comments — arriving just before his anticipated meeting with China’s Xi Jinping, which resulted in reduced tariffs on Chinese imports — appear to upend decades of American policy. The last US nuclear test was in 1992, before George HW Bush enacted a moratorium at the end of the Cold War.

Trump’s post was riddled with errors: Russia, not the US, has the world’s largest nuclear stockpile, and no country, with the exception of North Korea, is confirmed to have tested nuclear weapons since the 1990s, according to the UN. The US is also a signatory to the international treaty banning nuclear weapons tests, though has not ratified it.