North Korea threatened on Feb. 13 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, criticising 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.
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.
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."
