PYEONGCHANG (REUTERS) - South Korean President Moon Jae In met North Korean leader Kim Jong Un's sister on Saturday (Feb 10), hoping to translate Olympics detente into meaningful progress towards resolving a tense standoff over the North's nuclear and missile programmes.

Mr Moon hosted talks and a lunch with Ms Kim Yo Jong, the younger sister of the North Korean leader, at the presidential Blue House in Seoul.

Ms Kim Yo Jong flew in to the South on her brother's private jet on Friday before she and other North Korean officials attended the opening ceremony of the Winter Olympics in the alpine resort town of Pyeongchang.

Mr Moon and Ms Kim Yo Jong had their first face-to-face encounter at the opening ceremony. They shook hands and cheered for athletes from the two countries who marched under a unified peninsula flag for the first time in a decade.

Ms Kim Yo Jong is the first member of the ruling Kim family bearing the bloodline of the sacred Mount Paektu, a centrepiece of the North's idolisation and propaganda campaign, to cross the border into the South since the 1950-53 Korean War.

The 28-year-old is a crucial part of the North's Games delegation led by Mr Kim Yong Nam, North Korea's nominal head of state.

She shook hands with Mr Moon and smiled faintly as the South Korean leader entered a meeting room at the Blue House on Saturday.

"I appreciate you stayed late out in the cold, are you all well?" Mr Moon asked the delegation, before reporters were ushered from the room.

The delegations shared a lunch of dried pollack dumpling soup, a regional specialty of the only divided province on the Korean peninsula, and soju, a spirit popular on both sides of the heavily militarised border.

EXTREME PRESSURE

Mr Moon's desire to engage North Korea was in contrast to his US ally. US Vice President Mike Pence also attended the opening ceremony but had no contact with the North Korean delegation.

Some North Korean experts believe tough UN sanctions that are cutting off most of the isolated regime's sources of revenue might pressure Pyongyang to further engage with Seoul.

"I think this overture towards South Korea is partly sanctions-related, and also related to the fact that it's clear a divergence has developed between Washington and Seoul's most keenly desired goals in the near term," said Andray Abrahamian, a research fellow at Pacific Forum CSIS in Hawaii.

"The North Koreans should understand that for a summit or any kind of serious talks to occur, Moon needs to be able to take something to Washington - something that addresses denuclearisation," he said.

North Korea conducted its largest nuclear test last year and said it had developed a missile capable of carrying a warhead to the United States. US President Donald Trump and the North Korean leadership traded insults as tensions rose.

Mr Pence said the United States and South Korea were closely aligned in their approach to dealing with North Korea.

"I am very confident, as President Trump is, that President Moon will continue to stand strongly with us in our extreme-pressure campaign," Mr Pence told NBC in an interview, maintaining all options were open to deal with the crisis.

"Make no mistake about it, the United States of America has viable military options to deal with a nuclear threat from North Korea but, that being said, we hope for a better path," he said.

In Washington, China's top diplomat Yang Jiechi told Trump that China hoped it and the United States could increase their coordination on the North Korea issue. The United States has repeatedly pressed China, North Korea's most significant trading partner and main ally, to do more to rein in Pyongyang's nuclear and missile ambitions.

An official travelling with Japanese Prime Minister Shinzo Abe in Pyeongchang told reporters the Japanese government believed sanctions were "starting to bite", citing recent instances of ship-to-ship transfers at sea.

SACRED BLOODLINE

The two Koreas have a rocky and sometimes violent history at the Blue House. In January 1968, Ms Kim Yo Jong's grandfather, founding North Korean president Kim Il Sung, sent a squad of North Korean commandos to Seoul who tried unsuccessfully to kill then-president Park Chung Hee.

Although Ms Kim Yo Jong ranks diplomatically lower than Mr Kim Yong Nam, as Mr Kim Jong Un's sister she is considered more important in North Korea.

"By virtue of her family ties, Kim (Yo Jong) is among the most credible interlocutors that North Korea could have sent," said Christopher Green, a senior adviser on Korean affairs at the International Crisis Group think tank.

"If there is a message to be conveyed to South Korea or the US, she is amply well positioned to convey it," he said.

Ms Kim Yo Jong cuts a contrasting figure to her brother in North Korea's formal and tightly controlled state propaganda.

Rather than stand nervously around Mr Kim Jong Un on visits to official factories, she has moved to the front of media photos more recently, giggling, assisting her brother at state events or collecting flowers presented to him by young children.

She is also a vice director of the ruling Workers' Party's Propaganda and Agitation Department, which oversees and directs state censorship and propaganda.

It was that position which led the US Treasury Department to blacklist her last year for censorship and "severe human rights abuses".

The young North Korean leader and his sister were favourites of their father, who ruled North Korea from 1994-2011. Mr Kim Jong Il's sushi chef, Kenji Fujimoto, nicknamed them North Korea's "Prince" and "Princess" because of their upbringing and closeness to the former North Korean leader.