On Monday, the Pentagon put a dollar amount -- about $14 million -- on the costs of Freedom Guardian, a large-scale joint drill that was to kick off in August but which was shelved after Trump met with North Korean leader Kim Jong Un in a historic summit Singapore last month.

"We will be stopping the war games, which will save us a tremendous amount of money, unless and until we see the future negotiation is not going along like it should," Trump said after meeting Kim in a bid to solve the crisis over the North's nuclear weapons.

Trump later added on Twitter that the decision would "save a fortune."

The approximately $14 million is not an insignificant sum, but represents only a tiny portion of the Pentagon's $700 billion budget.

Pentagon spokesman Colonel Rob Manning, who disclosed the figure, did not provide a breakdown of how it was calculated.

Many of the costs associated with conducting large-scale drills are already baked into a military budget, as troops are continually training regardless of whether a formal exercise is underway.

America has about 28,500 troops based in South Korea and they routinely train with their local counterparts.

Freedom Guardian, which was to involve about 17,500 US troops, is usually an annual exercise that lasts two weeks. It is based on a computerized command-and-control drill that Pyongyang considers a highly provocative rehearsal for invasion.

Trump faced a backlash for scrapping the drills, with critics saying he gave in too readily to Kim's request to halt the exercises while getting little in terms of tangible commitments from Pyongyang in return.