North Korean leader Kim Jong-un has invited South Korea's president Moon Jae-in to a meeting in Pyongyang.

If taken up it would be the first time in a decade that the leaders of both countries have met for a summit.

Kim's sister Kim Yo Jong delivered the verbal invitation on Friday after arriving in Pyeongchang for the opening ceremony of the Winter Olympics.

Her presence helped the theme of Korean unity to dominate the opening ceremony as the two Koreas marched under one flag.

A spokesperson for President Moon said he hoped the two countries would work towards a summit and called on the US and North Korea to resume dialogue.

The US has been cautious about the invitation, with vice president Mike Pence also in South Korea to warn the country against "falling for" the North's overtures.

Pence did not directly address news of the invitation when asked.

A spokesperson said: "The vice president is grateful that President Moon reaffirmed his strong commitment to the global maximum pressure campaign and for his support for continued sanctions."

Kim's sister is said to be acting as his special envoy in the south during the Games.

During their meeting President Moon was pictured smiling and shaking hands with Kim Yo Jong.

Her presence in the Olympics Stadium in Pyeongchang is the first time that a member of her family have visited South Korea since the 1950-53 Korean War.

Tensions on the Korean border have escalated over the past year as the North pursues its ambition of becoming a fully-fledged nuclear power.