President Trump issued a cryptic warning Saturday as speculation mounts over whether he is planning military action against North Korea, saying "only one thing will work" when it comes to the ending the threat posed by the hermit nation.

"Presidents and their administrations have been talking to North Korea for 25 years, agreements made and massive amounts of money paid hasn't worked, agreements violated before the ink was dry, makings fools of U.S. negotiators," he tweeted. "Sorry, but only one thing will work!"

Presidents and their administrations have been talking to North Korea for 25 years, agreements made and massive amounts of money paid...... — Donald J. Trump (@realDonaldTrump) October 7, 2017

...hasn't worked, agreements violated before the ink was dry, makings fools of U.S. negotiators. Sorry, but only one thing will work! — Donald J. Trump (@realDonaldTrump) October 7, 2017

When asked by a reporter about the "one thing" while departing the White House, en route North Carolina, Saturday evening, Trump said only, "You'll figure that out pretty soon."

Trump gets asked on the South Lawn what is the one thing that will work with North Korea. His answer? “You’ll figure that out pretty soon." — Kaitlan Collins (@kaitlancollins) October 7, 2017

Trump warned that a "storm" is coming Thursday evening, which some have interpreted as a coded warning about a military conflict with North Korea. The White House downplayed the remark, calling it a "general comment."

Trump's secretary of state, Rex Tillerson, admitted last weekend that the U.S. has "lines of communication" with North Korea over its missile and nuclear weapons programs.

Trump later tweeted that he told Tillerson to stop "wasting his time" negotiating with the North Koreans. The president has also taken to mocking North Korea's leader, Kim Jong Un, with a new nickname: "little Rocket Man."

A number of Democrats hit back at Trump's tweets about North Korea, questioning his judgment on matters of national security.