The current joint U.S.-South Korean military exercises involve simulations of stabilizing North Korea after it has been occupied and conventional warfare has come to an end.

The U.S. and South Korea downsized the drills under a promise by U.S. President Donald Trump to North Korean leader Kim Jong-un in Singapore last year, so now they mostly consist of computer simulations.

Government sources here said the second part of the exercises beginning on Aug. 17 starts at an imaginary point 90 days after the outbreak of a war, when stabilization operations get underway.

The stabilizing drill has not been included in previous exercises which were based on the assumption that North Korea's military would be neutralized around 90 days after a war breaks out.

U.S. Defense Minister Mark Esper (right) walks with U.S. Forces Korea Commander Robert Abrams at Osan Air Base in Pyeongtaek, Gyeonggi Province on Thursday, in this photo tweeted by Esper.

But the current drills aim to check South Korea's readiness to take over wartime operational control of troops from the U.S. The two allies are keeping the exercises very quiet for fear of North Korea's reaction if it finds out that it involves mop-up operations inside its borders.

The drills started on Monday and simulate full-fledged battle after a North Korean invasion.

Officials here have still not disclosed the official name of the drills for fear of agitating the North, although it was earlier reported as simply "Alliance 19-2," for the sequential number and the year. It is unclear why they believe that the North would be particularly upset by the name.