Donald Trump has said there is no reason to spend a lot of money on war games with South Korea, but warned he could “instantly” relaunch the exercises and they would be “far bigger than ever before”.

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

But there was also a loaded message for Mr 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 Mr Trump’s attempted rapprochement with a long-time 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 US-South Korea war games,” Mr Trump said, citing what was presented as a White House statement.

“Besides, the president can instantly start the joint exercises again with South Korea, and Japan, if he so chooses. If he does, they will be far bigger than ever before.”

Mr Trump caught military leaders by surprise in June when he announced the suspension 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 invasion preparations. 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 exercises would foster goodwill and help nudge the North in the denuclearisation talks.

But beyond returning the apparent remains of about 55 US troops missing since the Korean War, and its continuing suspension in its missile and nuclear tests, there has been little movement from the North.

As a result, the US last week shelved a planned trip to Pyongyang by secretary of state Mike Pompeo, citing lack of progress on denuclearisation, but remaining open to future talks.

As doubts grow in Washington and beyond over Mr Kim’s willingness to relinquish his weapons, Mr Trump has been heaping blame on China, which is North Korea’s traditional ally and main trading partner.

On Wednesday, the president accused Beijing of pressuring the North because of tensions in US-China trade relations, and also of providing North Korea with money, fuel, fertiliser and other commodities, which he said was not helpful.

China co-operated with the US last year in adopting tough international sanctions against North Korea and maintains it is still enforcing the restrictions adopted by the UN Security Council.

But in his tweets, Mr Trump also signalled that the US has its own military means of exerting pressure on Pyongyang. His remarks compounded confusing messages from the Pentagon over the past two days that have revived speculation over the drills.

On Tuesday, defence secretary Jim Mattis told reporters the US might carry out drills with South Korea next spring after cancelling a major exercise this summer. He said no decision had been made on when to resume military exercises, but his statements suggested the recent cancellation might not be repeated.