North Korea issued a scathing personal attack Thursday on South Korean President Park Geun-Hye, accusing her of breaking a moratorium on cross-border insults and behaving like a "blabbering" peasant woman.

The attack referenced a speech Park made Monday at a nuclear summit in The Hague in which she voiced concern that Pyongyang's nuclear material could end up in terrorist hands, and warned of a possible Chernobyl-style disaster at the North's main Yongbyong atomic complex.

A spokesman for the North's Committee for the Peaceful Reunification of Korea (CPRK) said Park's remarks "violently trampled" on an agreement reached at rare, high-level talks last month for the two Koreas to stop "slandering" one another.

If Park genuinely wants to see improvements in inter-Korean relations, "she first has to stop rambling recklessly and learn how to speak with discretion", the spokesman said in a statement carried by the North's official KCNA news agency.

"Even if someone else wrote the dumb speech for her to read from, she should at least know what and what not to say... in order not to embarrass herself.

"She should realise she is no longer a peasant woman blabbering to herself in the corner of her room but the occupant of the (presidential) Blue House," he said.

North Korea has made similarly vitriolic attacks on Park in the past, but this was the first since last month's agreement.

North Korea had pushed hard for the "no slander" clause, which observers said was always going to prove problematic.

North Korea insists it should extend to the media and private groups and individuals, while South Korea argues that it cannot restrict freedom of speech.

Seoul denounced the CPRK statement as "rude" and unhelpful.

"We find the comments that can't even be repeated ... deeply regrettable and lacking the most basic etiquette," a government statement said.

The row came at a time of simmering military tensions on the Korean peninsula.

The North on Wednesday test-fired two medium-range ballistic missiles, as US President Barack Obama hosted a landmark Japan-South Korea summit aimed at uniting the three nations against Pyongyang's nuclear threat.

United Nations resolutions prohibit North Korea from conducting ballistic missile tests and the UN Security Council was set to hold closed-door consultations Thursday to discuss a possible condemnation of the latest launches.

"The North should immediately stop the acts of provocation that pour cold water on efforts...to create peace on the Korean peninsula and the region," the South Korean government statement said.