UN chief Ban Ki-moon said he is seeking a way to ease tensions between North and South Korea, and promised more help to Pyongyang to recover from deadly floods.

Ban, a former South Korean foreign minister, said inter-Korean relations had soured recently.

Cross-border relations have sharply worsened in recent months. The North has threatened "sacred war" against the South's conservative government for alleged insults to, and plots against, its regime.

The North is also grappling with the after-effects of floods that killed 169 people and left 400 missing.