For almost five hours, the North Korean drones flew above various South Korean cities, including Seoul, in the first such intrusion since 2017.
The military attempted to shoot down Pyongyang's drones by firing 100 rounds from a machine gun-equipped helicopter but failed to bring any down.
President reacts strongly
In response to Monday's incursions, South Korean President Yoon Suk-yeol demanded a stronger air defense system and cutting-edge stealth drones to monitor its reclusive neighbor more closely.
"The incident showed a substantial lack of our military's preparedness and training for the past several years, and clearly confirmed the need for more intense readiness and training," Yoon told a cabinet meeting.
"We have a plan to create a military drone unit tasked with monitoring key military facilities in North Korea. But we will advance the establishment of the drone unit as soon as possible because of yesterday's incident," he said.
"We'll also introduce state-of-the art stealth drones and bolster our surveillance capability."
South Korean military apologizes
The incident also prompted South Korea's military to apologize Tuesday for its failure to shoot down the drones. Seoul pledged to secure anti-drone strike capabilities.
It is exceedingly rare for South Korea to publicly admit reconnaissance operations inside of North Korea. Analysts suggest Yoon's determination to respond strongly to North Korean provocations is likely the reason.
Yoon, a conservative who took office in May, believes his liberal predecessor Moon Jae-in's policy of relying on Pyongyang's "good intentions" is to be blamed for the unpreparedness.
North Korean leader touts nation power
Meanwhile, across the border, leader Kim Jong Un opened a key political meeting with a report that touted North Korea's increased power in "in all fields of politics, military, economy and culture," the official Korean Central News Agency said on Tuesday.
At the Workers' Party plenary meeting in Pyongyang, which opened on Monday, Kim also urged for more efforts to address the difficulties and challenges facing his nation.
The plenary conference is expected to last several days, and later sessions are likely to feature Kim talking about things like his arms buildup, his ties with the United States, and the economy.