Seoul on Monday dismissed Pyongyang's denial of its responsibility for sending three drones across the border, reiterating that the communist state should stop its provocative acts and "groundless" slander against the South.
"Anyone who looks at the drones can be almost certain that the North is responsible for sending them. But the North is now denying it and it is inappropriate for it to continue slandering the South," Seoul's Defence Ministry spokesperson Kim Min-seok told reporters.
"The North is threatening peace and stability not only on the peninsula but also for the entire world."
Kim's remarks came after Pyongyang denied that it sent the apparent spy drones to the South, calling Seoul's claim a "fabrication" intended to slander Pyongyang.
The North's Committee for the Peaceful Reunification of Korea also reiterated that the South first violated an inter-Korean agreement to stop slandering one another, arguing that Seoul would pay dearly for it.
"(Seoul) is in a frenzy with its anti-Pyongyang propaganda and bashing campaign as it is now even fabricating the incident about the drones," the committee said in a statement carried by the North's official Korean Central News Agency.
"It brought to the fore its brutal mind with its fabrication of the Second 'Cheonan' incident by linking the drone case to us even when it said it had yet to find any critical evidence."
Pyongyang has long denied responsibility for a torpedo attack on the South Korean corvette Cheonan in March 2010 that killed 46 sailors.
Last Friday, Seoul announced the interim result of its probe into the drones, saying that they were "definitely" from the North. The authorities cited "circumstantial evidence" including their filming of South Korean military facilities.
Seoul has formed a scientific investigation team with Korean and US civilian experts to analyse data in the drones' memory chips containing "mission orders" that are expected to confirm the drones' departure points and travel routes.
The North's committee also berated President Park Geun-hye for her recent remarks on unification, calls for the North's denuclearization and failure to stop civilians from sending anti-Pyongyang leaflets into the reclusive state.
Despite the criticism, Seoul's Unification Ministry said that it would push for President Park's so-called Dresden Declaration, designed to lay the groundwork for reunification.
"We will show our sincerity about the Dresden proposals and continue to prepare for (the implementation of) the proposals," said ministry spokesperson Kim Eui-do during a regular briefing.
Regarding the North's repeated criticism of President Park, Kim said, "We feel no need to respond to every single statement (critical of Park)."
Pyongyang's stepped-up criticism of the Park government has further escalated military tensions on the peninsula, which have recently spiked due to the North's firing of ballistic missiles, the threat of another nuclear test and other saber-rattling moves.
Seoul's security authorities are carefully watching the North Korean military as Pyongyang could engage in additional provocations to show off its national pride both to domestic and international audiences during a set of national events this month.
The North on Tuesday is to celebrate the Day of the Sun, the birthday of late national founder Kim Il-sung, and the founding of the North Korean military next Friday.