SEOUL • The sister of North Korean leader Kim Jong Un is taking a leading role in a new, more hardline pressure campaign against South Korea, highlighting what analysts say is a substantive policy role that goes beyond being her brother's assistant.

Ms Kim Yo Jong, believed to be in her early 30s, is the only close relative of the North Korean supremo - said to be 36 years old - to play a public role in politics.

During the 2018-2019 flurry of international diplomacy, Ms Kim garnered global attention by leading a delegation to the 2018 Winter Olympics in South Korea.

Later, she was often seen dashing about to make sure everything went well for her older brother, including holding an ashtray for him at a train station while he was on his way to a summit with United States President Donald Trump in Vietnam.

But this year, Ms Kim has taken on a more public policy role, cementing her status as an influential political player in her own right.

"Prior to this, Ms Kim Yo Jong was portrayed in state media as Mr Kim Jong Un's sister, his protocol officer, or one of his accompanying officials," said Ms Rachel Minyoung Lee, a former North Korea open-source intelligence analyst in the US government.

"Now, North Koreans know for sure there is more to her than that," she added.

Ms Kim has worked behind the scenes in North Korea's propaganda agencies, a role that led the US to add her to a list of sanctioned senior officials in 2017 due to human rights abuses and censorship.

In March, state media carried the first-ever statement by Ms Kim, in which she criticised the South Korean authorities. It was followed by several more statements, including a response to comments made by Mr Trump.

Last Thursday, she issued a statement threatening to close the joint liaison office with the South.

On anti-North Korea leaflets flying over the border by balloon, Ms Kim accused South Korea of tolerating a "sordid and wicked act of hostility".

Ms Lee noted that Ms Kim's statements have a unique style, showcasing her wit and underscoring her powerful position.

"In addition to the harsh words and sarcasm, they can be bitingly witty in ways that the other statements are not," Ms Lee said.

"She seems to have more leeway in crafting her statements, which of course is not surprising."

When state media announced on Tuesday that the hotlines between the two Koreas would be severed, they said Ms Kim and a longtime hardliner, Mr Kim Yong Chol, championed the decision at a meeting.

This rare explanation of a policymaking process portrayed Ms Kim as "a very substantive person", said Mr Michael Madden, a North Korea leadership expert at the Stimson Centre, a US-based think-tank.

Mr Madden said this new portrayal of Ms Kim in state media may be a subtle dig at international analysts who have cast doubts on her ability to wield influence in the North's male-dominated society.

"They clearly have high hopes and expectations of her," he said.

"Not necessarily the next leader, but something of a kingmaker nonetheless."

REUTERS, BLOOMBERG