The president made the dramatic revelation during a briefing Thursday, hours after revealing that North Korea has already returned the remains of 200 USA troops missing from the Korean War.
In reality, the statement going along with the executive order is practically a form letter, closely mirroring what is issued annually since the Bush-era as a justification to give the executive branch power to impose a series of sanctions on North Korea.
However, he also tweeted that, "Everybody can now feel much safer than the day I took office".
The action was pro forma, but notable for the stern tone and list of accusations against North Korea just 10 days after the warm meeting between Trump and Kim.
Of those, an estimated 5,300 are believed to be in North Korea.
'They've already blown up one of their big test sites, in fact it's actually four of their big test sites'.
After President Donald Trump held a summit with North Korean leader Kim Jong-un - a meeting that was by most accounts a dismal failure of strategy- he made a bold declaration that was surprising, even for him.
"The report of President Trump's own administration completely undercuts his statements over the last few weeks", said the Senate's top Democrat, Chuck Schumer.
If not, verification will have to rely on DNA analysis according to very strict protocols observed by the USA military for missing soldiers.
At the Pentagon Wednesday, Mattis was asked whether North Korea had begun dismantling its nuclear and ballistic missile programs.
Repeating North Korean arguments, Trump said the games were "provocative" to Pyongyang and added that they were "very expensive".
But the regional mood has turned towards diplomacy since the Winter Olympics in South Korea earlier this year, which set off a series of diplomatic moves culminating in the Trump-Kim meet.
"To support implementing the outcomes of the Singapore Summit, and in coordination with our Republic of Korea ally, Secretary Mattis has indefinitely suspended select exercises", Pentagon spokeswoman Dana White said.