North Korean leader Kim Jong-un said South Korea is a foreign and hostile nation, state media KCNA reported on Friday, with photos showing Kim conferring with high-ranking soldiers.

Kim discussed the use of "offensive forces" against the South as retaliation for any move that infringes on its sovereignty, the report said.

There was no elaboration on what forces might be used.

The report comes a day after KCNA said North Korea amended its constitution to designate the South as a "hostile state".

Kim has increasingly lashed out at South Korea this year, accusing Seoul of colluding with Washington to seek the collapse of his regime and has pushed for a clear break with decades of policy engagement with the South, including the scrapping of unification as a goal.

The reclusive state blasted road and rail links with South Korea this week.

Those actions underscored "not only the physical closure but also the end of the evil relationship with Seoul," KCNA quoted Kim as saying.

Seoul has said that if North Korea were to inflict harm upon the safety of its people, "that day will be the end of the North Korean regime."

Kim made the remarks while inspecting the headquarters of the 2nd Corps of the North Korean army on Thursday, KCNA said, a major military unit that includes several forward-deployed brigades with heavy weapons aimed at the South.

During the visit, he also said the changed nature of the South Korea-US alliance and their different, more developed military manoeuvres, highlight the importance of a stronger North Korean nuclear deterrent. (Reuters)