WASHINGTON -- President Donald Trump said Wednesday that there's no reason to spend a lot of money on military wargames with South Korea, but warned he could "instantly" relaunch the exercises again and they would be "far bigger than ever before."

Trump made the comment in a series of tweets that primarily took aim at China, blaming it for lack of progress on getting North Korea to end its nuclear program, following the president's landmark summit with Kim Jong Un in June.

But there was also a loaded message for Kim: mixing an expression of goodwill to the North Korean autocrat with an implicit military threat that will add to speculation over the direction of Trump's attempted rapprochement with a longtime adversary.

"The President believes that his relationship with Kim Jong Un is a very good and warm one, and there is no reason at this time to be spending large amounts of money on joint U.S.-South Korea war games," Trump said, citing what was presented as a White House statement.

On Tuesday, Defence Secretary Jim Mattis told reporters the U.S. might carry out military exercises with close ally South Korea next spring after having cancelled a major exercise this year. Mattis said no decision has been made on when to resume military exercises, but his statements suggested the recent cancellation might not be repeated.

Trump caught military leaders by surprise in June, when he announced the suspension of exercises with the South, "unless and until we see the future negotiation is not going along like it should." He called the drills costly and provocative.

The cancellation was an olive branch to Pyongyang, which has long complained that the exercises were threatening. Often the North has reacted to the exercises with its own demonstrations of military might, including firing a new intermediate-range missile over Japan last year as a countermeasure to the drills.

There was some hope that the gesture of shelving the fall exercises would foster goodwill and help nudge the North in the denuclearization talks. But beyond returning the potential remains of about 55 U.S. troops missing from the Korean War, there has been little movement from the North.

As a result, the U.S. last week shelved a planned trip to Pyongyang by Secretary of State Mike Pompeo, citing lack of progress on getting the authoritarian regime to abandon its nuclear weapons, as agreed upon at the Trump-Kim summit in Singapore.