North Korea threatened on Friday a "terrible response" if it detects any more drones buzzing across the border from the South.
South Korean President Lee Jae Myung has sought to repair ties with North Korea since taking office last year, criticizing his predecessor for allegedly sending drones to scatter propaganda over Pyongyang.
But North Korea claims it shot down a surveillance drone just last month, an incident which threatens to blight Lee's efforts to patch things up.
Kim Yo Jong, the powerful sister of North Korean leader Kim Jong Un, warned of severe repercussions if the drones did not stop.
"I give advance warning that reoccurrence of such provocation as violating the inalienable sovereignty of the DPRK will surely provoke a terrible response," Kim said in a statement carried by Pyongyang's official Korea Central News Agency.
"We don't care who the very manipulator of the drone infiltration into the airspace of the DPRK is and whether it is an individual or a civilian organization," she added, using the acronym for North Korea's official name.
Seoul initially denied any official involvement in the January drone incursion, with officials suggesting it was the work of civilians.
But a joint military-police task force announced earlier this week it was investigating three active-duty soldiers and one spy agency staffer in an effort to "thoroughly establish the truth".
Seoul's unification minister Chung Dong-young expressed "deep regret" earlier this week.
Any government involvement in the January drone incursion would run counter to Lee's efforts to lower the temperature with Pyongyang.
Chung has previously suggested the drone may have been the work of government staffers still loyal to former hardline leader Yoon Suk Yeol.
Kim Yo Jong said that Chung's conciliatory remarks were "quite sensible behavior".
South Korea's unification ministry responded to Kim's statement, vowing to "immediately implement preventative measures to prevent similar incidents from recurring."
"Whenever the opportunity arises, we have reaffirmed three principles -- recognizing and respecting the other side's system, refraining from any hostile acts, and not seeking unification by absorption," it said.
The statement by Kim Yo Jong suggests that Pyongyang is "closely monitoring the latest developments in the South Korean side", Yang Moo-jin, former president of the University of North Korean Studies, told AFP.
The North Korean military downed a drone carrying "surveillance equipment" in early January, according to a statement published by the state-run KCNA.
Photos showed the wreckage of a winged craft scattered across the ground next to a collection of grey and blue components that allegedly included cameras.
The drone had stored footage of "important targets" including border areas, a military spokesman said at the time.
South Korea's disgraced ex-president Yoon Suk Yeol was accused of using unmanned drones to scatter propaganda leaflets over North Korea in 2024.
Lee has vowed to mend ties with North Korea by stamping out such provocations, and has even suggested a rare apology may be warranted.
A UN Security Council committee recently approved exemptions allowing fresh flows of food and medicine into North Korea.
Analysts said this could kickstart efforts to lure Pyongyang into nuclear negotiations with US President Donald Trump.
