Trump says Russia, China conduct nuclear tests but 'don't talk about it'

US President Donald Trump alleged Sunday that nuclear-armed countries including Russia and China have conducted underground nuclear tests unknown to the public.

"Russia's testing, and China's testing, but they don't talk about it," he said in an interview with CBS's "60 Minutes" program, when asked about his surprise order on Thursday for the United States to test nuclear weapons.

"You don't necessarily know where they're testing... They test way underground where people don't know exactly what's happening with the test," he added.