The influential sister of North Korean leader Kim Jong-un is to attend Friday's opening ceremony of the Winter Olympic Games, which are being held in the South, ministers in Seoul say.

Kim Yo-jong is the youngest daughter of late leader Kim Jong-il and her role was strengthened last year when she was promoted to the politburo.

Both Koreas will march under one flag at the opening ceremony.

The North's participation has been seen as a thawing of bilateral ties.

However, experts say it is unlikely to have any impact on the North's nuclear ambitions.

The US believes the North is using the Olympics for propaganda purposes and is sending Vice-President Mike Pence to the opening ceremony in Pyeongchang to counter it.

"We're travelling to the Olympics to make sure that North Korea doesn't use the powerful symbolism in the backdrop of the Winter Olympics to paper over the truth about their regime," he said.