South Korea says the North is unlikely to have been involved in the sinking of one of its navy vessels near their disputed border.

South Korea's defence ministry says the vessel was well south of the disputed border between the two Koreas and there were no North Korean ships in the area at the time of the accident.  The warship sank on Friday evening after an explosion destroyed most of of its rear. The exact cause of the blast is not yet clear. The defence ministry says 58 of the ship's 104 crew have been rescued while 46 are still missing.

The North refuses to accept the maritime border known as the Northern Limit Line, which was drawn up by United Nations forces after the 1950-53 Korean War.  Last November, the navies of the two nations exchanged fire in the area.

Despite an armistice agreement, a peace treaty was never concluded and officially the North and South remain at war.