ISTANBUL 

US President Donald Trump announced Thursday that he has instructed the Defense Department to “immediately” begin nuclear weapons tests.

"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 wrote on his Truth Social platform, referring to his rebranded name for the department.

Stressing that the US has "more Nuclear Weapons than any other country," he said this was accomplished during his first term, including "a complete update and renovation of existing weapons."

He warned, however, that the US’s adversaries are catching up.

"Because of the tremendous destructive power, I HATED to do it, but had no choice! Russia is second, and China is a distant third, but will be even within 5 years," he said.

Trump’s post came while returning from South Korea, where he had met Chinese President Xi Jinping.

Speaking to reporters aboard Air Force One, he said the decision was related to the actions of the other nuclear-armed nations, which “seem to all be nuclear testing.”

“We have more nuclear weapons than anybody. We don't do testing. We’ve halted it years, many years ago. But with others doing testing, I think it's appropriate that we do also,” he added.

*Ahmet Salih Alacaci in Washington DC, contributed to this report