North Korea has threatened to attack South Korean loudspeakers broadcasting anti-Pyongyang propaganda messages across their shared - and the world's most heavily armed - border.

The warning follows Pyongyang's earlier denial that it had planted landmines on the South Korean side of the Demilitarised Zone that injured two South Korean soldiers last week.

Seoul retaliated for those injuries by restarting the loudspeaker propaganda broadcasts for the first time in 11 years and suggested more actions could follow.

The authoritarian North is extremely sensitive about external insults of its leader, Kim Jong Un, and tries to isolate its people from any criticism or suggestions that the leadership is anything other than powerful and revered.

North Korea's army said in a statement that the broadcasts were equivalent to a declaration of war and that a failure to immediately stop them and take down the loudspeakers would result in "an all-out military action of justice to blow up all means for 'anti-north psychological warfare'" on the front lines.

Such bombast is not unusual and it is not the first time Pyongyang has threatened to attack its enemies. Seoul is often warned that it will be reduced to a "sea of fire" if it does not do as the North bids, and Washington and Seoul were both threatened with nuclear annihilation in the months after Kim took power in late 2011.

Pyongyang's threats are rarely backed up, although the North did launch an artillery attack in 2010 that killed four South Koreans. Later that year, a Seoul-led international investigation blamed a North Korean torpedo for a warship sinking that killed 46 South Koreans.

Responding to the claims by Seoul and the US-led United Nations Command that North Korean soldiers buried the landmine explosions, North Korea's powerful National Defence Commission argued that Seoul fabricated the evidence and demanded video proof to support the argument that Pyongyang was responsible.

The explosions resulted in one soldier losing both legs and another soldier one leg.

Officials said the mine planting violated the armistice that stopped fighting in the 1950-53 Korean War, which still technically continues because there has never been a formal peace treaty.

South Korea's President Park Geun-hye said her government would respond firmly to any North Korean provocation that threatens the safety of South Koreans.

She urged Pyongyang to "wake up" from the delusion that it could maintain its regime with provocation and threats, which she claimed would result only in the North's isolation and destruction.

Ms Park said that if the North opted for dialogue and co-operation, it would find opportunities to improve the lives of its people. She also urged the North to accept the South's proposals for building a "peace park" in the demilitarised zone and family reunions.

PA Media