Officials in South Korea are calling for caution amid reports that North Korean leader Kim Jong-un has died after a botched heart surgery or may be severely ill, emphasising that they have detected no unusual movements across the border in the north.

At a closed-door forum on Sunday, South Korea’s Unification Minister Kim Yeon-chul, who oversees engagement with the North, said the government has the intelligence capabilities to say with confidence that there was nothing unusual happening, Al Jazeera reported.

Rumours and speculation over the North Korean leader’s health began after he did not appear at a key state holiday on April 15. He has not been seen in public since.

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READ: North Korean dictator Kim Jong-un reportedly dead after botched heart surgery

“Our government’s position is firm,” Moon Chung-in, a special adviser on national security to the South Korean president, Moon Jae-in, said in an interview with CNN on Sunday. “Kim Jong-un is alive and well.”

The adviser said that Kim had been staying in Wonsan – a resort town on the country’s east coast – since 13 April, adding, “No suspicious movements have so far been detected.”

“We have nothing to confirm and no special movement has been detected inside North Korea as of now,” the South’s presidential office said in a statement last week.

Speculation about Kim grew after Daily NK, a Seoul-based online media outlet that employs North Korean defectors, claimed he was recovering after undergoing a “cardiovascular procedure” earlier this month.

Citing a single unidentified source inside the country, it said Kim, who is believed to be 36, had required urgent treatment due to heavy smoking, obesity and fatigue.

Soon afterwards, CNN reported that Washington was “monitoring intelligence” that Kim was in “grave danger” after undergoing surgery, quoting what it said was an anonymous US official.

Meanwhile, it has also been reported that Kim has sent a message of gratitude to workers building a tourist resort in Wonsan.