Roads and Transport Authority has been working round the clock to carry out maintenance work
"This suggests the possibility of expanding her status and role as official successor," the report said.
The report comes amid media speculation that Jong-un might be seriously ill.
Unconfirmed rumours spiked after he skipped an annual visit to the mausoleum of his grandfather Kim Il-sung on the late national founder's April 15 birth anniversary, the North's most important national holiday, Yonhap News Agency reported.
"Kim Yo-jong has virtually taken on the role of the party's core, undertaking the responsibility of the party's monolithic leadership system." the report said.
Her ascent to supreme leadership, if it were to take place, would not occur immediately, the think tank forecast, adding that an official process would be required after Kim Jong-un returns to the spotlight.
The report noted Kim Yo-jong's official statements toward South Korea and the United States in place of her brother earlier this year as some of her recent major activities.
First seen in public during the funeral of late leader Kim Jong-il in 2011, Kim Yo-jong's public profile has been quite visible in the past two years.
She was spotted near her brother at summit events with South Korean President Moon Jae-in and US President Donald Trump.
Roads and Transport Authority has been working round the clock to carry out maintenance work
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