South Korea and the United States have not yet decided when and how to conduct an annual summertime exercise, the defense ministry said Monday, after North Korea warned the drills will cloud the future of inter-Korean ties.

On Sunday, Kim Yo-jong, the powerful sister of the North's leader Kim Jong-un, issued a statement saying that the combined exercise could undermine efforts to improve inter-Korean relations at "such a crucial time" after the long-severed cross-border communication lines were restored last week.

Defense ministry spokesman Boo Seung-chan said when and how to stage the drills have yet to be finalized, adding that they are issues to be decided by Seoul and Washington.

"South Korea and the US are having close consultations taking into account related situations," Boo told a regular press briefing, citing the pandemic, a combined defense posture, the transfer of wartime operational control and denuclearization efforts as some of the factors being taken into consideration.

The annual summertime military exercise, usually held in August, has been a focus of attention amid concern it could negatively affect a conciliatory mood created in the wake of the restoration of inter-Korean communication channels.

Pyongyang has long bristled at such combined drills, branding them as a rehearsal for invasion.

"Our government and army will closely follow whether the South Korean side stages hostile war exercises in August or makes other bold decision," Kim said in Sunday's statement.

On Friday, Defense Minister Suh Wook held phone talks with his US counterpart Lloyd Austin and reaffirmed their commitment to a posture of strong combined readiness.

Asked if Seoul could propose holding inter-Korean defense talks to discuss the issue, Boo said they have no such plans for now. (Yonhap)