North Korea has exposed that one of its warships sank last month, killing a number of sailors, in what is said to be a rare admission of military failure.

State media reported a visit by leader Kim Jong-un to a naval cemetery for the crew of "submarine chaser No 233".

The report said the vessel had been performing combat duties but gave no more information about what happened.

According to state news agency KCNA, “Submarine chaser No 233 fell while performing combat duties in mid-October raid’’.

Images showed Mr Kim, accompanied by several officials, visiting a memorial which included multiple gravestones with images inscribed on them.

North Korea has a large military but much of its equipment is believed to be old and out of date.

Reports in South Korean media, citing unidentified sources, suggested age could have been a factor in the sinking.

These reports said the incident was believed to have taken place off Wonsan, on the east coast of the Korean peninsula, during an exercise.

The two Koreas remain technically at war, following the Korean conflict which ended in a truce rather than a peace treaty.