President Donald Trump called on US military leaders to resume testing US nuclear weapons in order to keep pace with other countries such as Russia and China, BBC reported.

"Because of other countries testing programs, I have instructed the Department of War to start testing our Nuclear Weapons on an equal basis," he wrote on social media just before meeting with Chinese President Xi Jinping in South Korea.

The US has more nuclear weapons than any other country, Trump said, with Russia second and China a "distant third". It has not conducted nuclear weapons testing since 1992, according to BBC.