South Korean troops were set on Friday to finish the 12-day Hoguk 22 field exercises, which have included some drills with US troops, while South Korean and US aircraft are due to begin major drills on Monday.
North Korea has said its recent missile launches were in protest against the joint exercises, which it says are provocative and a rehearsal for an invasion.
South Korea and the US say the exercises are defensive and needed to counter the North’s threats.
The US and its allies believe the North could be about to resume nuclear bomb testing for the first time since 2017.
South Korean President Yoon Suk-yeol has said the North has completed all the technical preparations needed for an underground blast at its Punggye-ri test site, which has been officially shuttered since 2018.
North Korea held six nuclear tests there from 2006 to 2017.
A seventh North Korean nuclear test would be further “confirmation of a programme which is moving full steam ahead in a way that is incredibly concerning,” the head of the United Nations nuclear watchdog said on Thursday.
South Korea has warned that a resumption of the North’s nuclear testing would have to be met with an “unparalleled” response from the allies, but neither it nor the US has given details.