Image copyright Reuters

Over the past few years, Kim Yo-jong has emerged as a key figure in Pyongyang's opaque architecture of power.

She is the younger sister of Supreme Leader Kim Jong-un and the only one of his siblings considered a close and powerful ally.

Kim Yo-jong first gained international attention in 2018, when she was the first member of the Kim dynasty to visit South Korea. She was part of the delegation to the Winter Olympics, where North and South competed as a joint team.

The 2018 thaw which followed saw her working alongside her brother as he set off on an international diplomacy path, meeting South Korean President Moon Jae-in, China's Xi Jinping and most importantly US President Donald Trump.

The close relationship with her brother and her increasingly senior roles in the political apparatus put her once again in focus in April 2020 during a period when Kim Jong-un seemed unusually absent from any public events.

When Mr Kim's temporary disappearance in April prompted questions about his health, she was touted to be among the top ranks of people to succeed him.

Ms Kim's role was first boosted in October 2017 when she was promoted to the powerful politburo. Before that, she'd been influential as vice-director of the propaganda and agitation department - a role she is thought to still hold and where she works on her brother's public image in the country.

Image copyright Getty Images Image caption Ms Kim has been party to her brother's diplomatic talks, here with South Korea's Moon Jae-in

Ms Kim is also on the US sanctions list over her alleged links to human rights abuses in North Korea. That means US citizens are prohibited from conducting any transactions with her. Any property and assets in the US would be frozen.

How powerful is she?

It is notoriously difficult to understand the power mechanisms in North Korea and therefore it's hard to gauge how much of her own political network Kim Yo-jong has.

She is rumoured to be married to the son of Choe Ryong-hae, the powerful party secretary and effectively Kim Jong-un's second in command. If true, that would give her significant status.

Oliver Hotham, of NK News, told the BBC that "given she's a 30-something woman - which is not a demographic that typically has a great deal of power in North Korea - most of her influence derives from who her brother is".

More recently, she has been responsible for delivering several strongly-worded messages against the South and has emerged as North Korea's new point-person on inter-Korean affairs, according to NK News.

In June, Kim Yo-jong threatened to send troops into the demilitarised zone (DMZ) at the inter-Korean border, in part because of what Pyongyang said was Seoul's failure to stop activists sending anti-regime leaflets over the border.

She also warned that the inter-Korean liaison office near the border town of Kaesong in the North, which Pyongyang withdrew from in March 2019, would be "collapsed".

Media playback is unsupported on your device Media caption South Korea released military footage of the explosion in the border town of Kaesong

Days later, on 16 June, a loud explosion was heard in Kaesong and smoke was seen billowing from the area. Officials in Seoul confirmed that the office, which the South Korean government had provided nearly $8m (£6.3m) towards refurbishing, had been demolished.

What's behind the Kim family bloodline?

Should there be a need to find a successor for Kim Jong-un, family ties will be crucial.

The country's propaganda and political mythology has for decades stressed the so-called Paektu bloodline going back to state founder Kim Il-sung. Kim Jong-un is believed to have children, but they are young.

Given that Ms Kim is a member of that bloodline, state media should find it easy to justify a transition of power into her hands. But that bloodline also means that were she not chosen, any new leader would see her as a dangerous rival.

"Unless another member of the Kim family comes in charge, for her the things will be very simple," says Fyodor Tertitskiy of Kookmin University in Seoul. "Either she takes the mantle of the Supreme Leader or loses all power and potentially her life as well."

Where does she fit in the ruling family?

Kim Yo-jong is the youngest daughter of late leader Kim Jong-il. She shares the same mother as Kim Jong-un and Kim Jong-chol, the brother who is thought to be not very senior in the political power system.

Born in 1987 she is four years younger than her brother Kim Jong-un. The two of them lived and studied in Berne, Switzerland, at the same time.

Image copyright Getty Images Image caption The two are the youngest children of the late Kim Jong-il

School officials in Switzerland have said she was over-protected by the coterie of guards and caretakers. She once reportedly had a mild cold and was immediately pulled from school and taken to hospital.

Reports say she has had a sheltered upbringing, and most members of the Kim family have not interacted with her much.

What does she do?

Since 2014, Kim Yo-jong's main job has been to protect her brother's image, taking up a key role in the party's propaganda department. When in 2017 she was elevated to an alternate member of the politburo, this seemed to indicate a shift in seniority although her main role remained in propaganda.

She is said to have managed all his public appearances as well as acting as a political adviser.

When the Hanoi summit in 2019 failed to result in an agreement with the US, it's thought she might have been somewhat demoted from the politburo - and only in early 2020 was she reinstated to that body.

Before 2014, she'd only sporadically been in the spotlight, appearing at the state funeral of her father in 2011 and the election of her brother in 2014. Ms Kim has occasionally been seen with her brother in state media pictures.

Yet a top job in the leadership is thought to have been carved out for her as early as 2008 during succession planning when Kim Jong-il's health deteriorated.

Her role as possible successor to her brother has surfaced every time there was uncertainty about Kim Jong-un.

Just like in April 2020, there were similar rumours in 2014 when Kim Jong-un had disappeared from public view only to re-emerge in decent health albeit aided by a walking stick.