North Korean state news agency KCNA on Thursday reported for the first time that the country had revised its constitution to define South Korea as a "hostile state."

The change took place last week at a meeting of the country's rubber-stamp legislature, following a proposal from Kim Jong Un in January, but past propaganda on revisions to the constitution had offered few details.

KCNA say blowing border links was 'inevitable and legitimate measure' given new status

The new status was mentioned in a KCNA report on North Korea detonating symbolic roads and railways still linking it to the South two days earlier.

The state-controlled news agency said that the army had taken "a measure to physically cut off the DPRK's roads and railways which lead to the ROK [South Korea]" which was "part of the phased complete separation of its territory, where its sovereignty is exercised, from the ROK's territory."

North Korea's formal name is the Democratic Republic of Korea (DPRK) and South Korea's the Republic of Korea (ROK).

KCNA reported that the destruction of connecting infrastructure was an "inevitable and legitimate measure taken in keeping with the requirement of the DPRK Constitution which clearly defines the ROK as a hostile state."

KCNA also published unverified images it said depicted the detonations, which took place at a closed event without international journalists present. (Deutsche Welle)

North Korea's Supreme People's Assembly had convened last week and KCNA had made mention of amendments to the constitution without offering many details.

This passing reference on Thursday, which also went into no further detail, was its first confirmation of the change.

An 'expected' confirmation

In January, Kim had called for a constitutional amendment to erase reunification with the South as a national goal while accusing Seoul of colluding with the US to seek the collapse of his regime.

"There may still be an internal propaganda review underway about the appropriate way to disclose the constitutional revisions, but this confirmation was expected," Ankit Panda, an expert with the Carnegie Endowment for International Peace, told the Associated Press.

In response, South Korea has said it will continue to pursue reunification but will respond to any mounting aggression with force. It fired warning shots south of the border when the North detonated the roads and railways.

Some experts warn this could be Kim making legal room to use nuclear weapons against the South by legally defining it as an enemy state.

Others say he may instead be seeking to guard against South Korean culture and cement his family's grip on power closer to home, given the vast and still widening gap in living standards in the two countries.

Worsening relations

Animosity between the two neighbors increased over the last few days when Pyongyang accused Seoul of flying drones over it three times this month, warning of military reprisals in the future.

While the South initially denied claims about the drones, it later changed tactics and refused to comment.

Moreover, Pyongyang has increased testing of nuclear-capable ballistic missiles over the last year which it says is in response to military drills and collaboration between South Korea and the nuclear-armed US.

Formally, the two countries have been in a state of war since 1950 as the Korean War concluded with an armistice rather than peace treaty in 1953.