AFP takes a look at what we know:

What has changed?

For decades, North Korea was officially committed to reunification, and in their constitutions, both North and South Korea claim sovereignty over the whole of the peninsula.

But in January, the North's leader Kim Jong Un declared South Korea his "principal enemy", cut all communications to an "irretrievable level", and had mentions of "reconciliation" or "fellow countrymen" scrubbed from record.

Since then, the North has ramped up weapons testing, bombarded the South with trash-carrying balloons, threatened war over drone incursions, and blown up roads and railways connecting the countries.

"North Korea is simply following through on what they said they would do," Lim Eul-chul, a professor at Kyungnam University, told AFP.

"It seems to reflect the North's determination to completely eliminate any premise of 'unification by absorption' into the South."

Kim even said recently that his country was no longer interested in "liberating the South".

Why now?

It might be the weather.

Swathes of North Korea were hit by devastating floods this summer that destroyed thousands of homes and farms, killing and displacing people.

Pyongyang could have orchestrated this latest round of conflict with the South to deflect from growing domestic discontent, Seoul officials have said.

The North's claims that Seoul flew drones over Pyongyang -- a major security breach -- have appeared on the front pages of the country's tightly controlled state media.

This is a bid to rally "North Korean citizens, who have grown weary of the fake dictatorship of the Kim family", South Korea's military has said.

Seoul's national security adviser Shin Won-sik said "North Korea is escalating tensions in order to tighten its grip over its unstable internal affairs".

"North Korea is a regime that, paradoxically, maintains its stability by the existence of external threats to its system," he added in a state broadcast interview.

What about the drones?

The North says South Korea's military has been flying drones over the capital Pyongyang to drop anti-regime propaganda -- a "remarkable" development which "showcases one of the pathways through which we could see a serious bout of escalation between the two countries," US-based analyst Ankit Panda told AFP.

North Korea, which lacks robust air defences, is insecure about the incursions.

"Drones over their national capital could provide the kind of reconnaissance in a time of war that would allow the South Koreans to strike directly at Kim Jong Un himself," he said.

Cheong Seong-chang, director of the Korean peninsula strategy at Sejong Institute, said the reports suggest "the breach was detected in the airspace above the headquarters of the Central Committee of the Workers' Party of Korea".

"The North Korean leadership would have been greatly shocked," he told AFP.

Even if these drones were just dropping propaganda rather than seeking to locate Kim's office, it is still a problem as the country regards all "foreign content as a subversive threat", said Leif-Eric Easley, a professor at Ewha University in Seoul.

But Seoul's military has pointed out that the North has repeatedly sent drones into the South -- including to Seoul's district of Yongsan, where the presidential compound is located, in 2022.

Is Russia involved?

Historic allies Russia and North Korea have drawn ever closer since Moscow invaded Ukraine in February 2022.

Seoul claims Kim has been shipping arms to Moscow to use against Kyiv, and Ukrainian President Volodymyr Zelensky recently accused the North of sending troops to Russia's army.

After the North blew up inter-Korean roads and railways, ally China urged all sides to avoid escalation. But Russia blames Seoul for the drones, saying it was a "gross encroachment on the sovereignty" of North Korea.

"Russia and North Korea are not only engaging in sanctions-violating military trade and reviving Cold War-era diplomatic commitments," said Easley.

"They are also reinforcing and amplifying each other's political propaganda in attempts to justify and normalise their pariah state behaviour."

Have they done this before?

North and South Korea have long been locked in cycles of escalation, and Pyongyang has repeatedly blown up key infrastructure in the past to make foreign policy points.

In 2008, it blew up a cooling tower at a nuclear complex after the United States agreed to remove Pyongyang from its list of states that sponsor terrorism.

In 2018, after it signed a tension-reducing military deal with the South, it simultaneously detonated 10 guard posts.

After diplomatic outreach broke down, it then blew up a liaison office in 2020, largely out of frustration that activists in the South were sending balloons carrying anti-regime propaganda leaflets across the border.