Kim Jong-un is “alive and well”, a senior South Korean presidential aide has insisted amid fervent speculation about the authoritarian ruler's health.

North Korea has done little to dispel rumours which began a fortnight ago, when the country's leader missed an annual commemoration for his grandfather for the first time since assuming power in 2011.

Speculation reached fever pitch as Reuters reported China had sent a team on including medical experts to advise on Mr Kim on Thursday, days after a report by the Seoul-based Daily NK newspaper cited an anonymous source who claimed he the leader had undergone heart surgery.

Social media has since fuelled reports that Mr Kim is seriously unwell or even possibly dead.

On Sunday, however, a senior foreign policy adviser to South Korea’s president Moon Jae-in poured cold water on those claims.

Kim Jong-un: Power in pictures Show all 20 1 /20 Kim Jong-un: Power in pictures Kim Jong-un: Power in pictures Kim Jong-un rides a horse during snowfall in Mount Paektu in this image released by North Korea's Korean Central News Agency on 16 October 2019 Reuters Kim Jong-un: Power in pictures Kim Jong-un visits the newly built Pyongyang Orphans' Primary School on 2 February 2017 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un inspects a women's company under Unit 5492 of the Korean People's Army in November 2019 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un inspects the test-fire of intercontinental ballistic missile Hwasong-14 at an undisclosed location in July 2017 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un celebrates the successful test-fire of the intercontinental ballistic missile Hwasong-14 at an undisclosed location in July 2017 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un inspects a potato at the Samjiyon Potato Factory in North Korea in October 2018 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un rides a horse through a forest in this image released by North Korea's Korean Central News Agency on 16 October 2019 EPA Kim Jong-un: Power in pictures Kim Jong-un inspects a block of frozen fish at a processing facility in North Korea in November 2018 Reuters Kim Jong-un: Power in pictures Kim Jong-un celebrates the succeful launch of a strategic submarine-launched ballistic missile in August 2016 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un shakes hands with Donald Trump as they meet for the first time at the Capella Hotel on Sentosa island in Singapore in June 2018 Reuters Kim Jong-un: Power in pictures Kim Jong-un and Donald Trump share a glance as they meet in the Demilitarised Zone in Panmunjon, Korea in June 2019 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un inspects mushrooms at Pyongyang Mushroom Farm AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un inspects a super-large multiple rocket launcher ahead of a test in September 2019 Reuters Kim Jong-un: Power in pictures Kim Jong-un inspects an apple farm in South Hwanghae Province in September 2017 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un inspects an apple farm in South Hwanghae Province in September 2017 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un inspects dental wares at a newly built factory in June 2017 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un visits Farm No 1116 in September 2017 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un visits a motor factory in November 2017 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un rides a horse during snowfall in Mount Paektu in this image released by North Korea's Korean Central News Agency on 16 October 2019 AFP/Getty Kim Jong-un: Power in pictures Kim Jong-un inspects the Command of the Strategic Force of the Korean People's Army at an undisclosed location in August 2017 AFP/Getty

“Our government position is firm,” Chung-in Moon told Fox News. “Kim Jong Un is alive and well. He has been staying in the Wonsan area since 13 April. No suspicious movements have so far been detected.”

Seoul has repeatedly indicated there have been no unusual signs that could indicate health problems for Mr Kim – whose well-known propensity for cigarettes, apparent weight gain and family history of heart problems has fuelled speculations.

Mr Chung-in’s suggestion that the North Korean leader may be staying out of Pyongyang was lent further credence on Saturday by satellite images published by 38 North, a website specialising in North Korea studies.

The pictures showed a train likely belonging to Mr Kim has been parked at his Wonsan compound on the country’s east coast since at least 21 April. It had not been present on 15 April, the website's researchers said.

“The train’s presence does not prove the whereabouts of the North Korean leader or indicate anything about his health, but it does lend weight to reports that Kim is staying at an elite area on the country’s eastern coast,” they added.

Many experts in South Korea have downplayed speculation that Mr Kim is seriously ill.

They also suggested North Korea was unlikely to face serious immediate turmoil if Mr Kim was incapacitated or died because someone such as his influential sister Kim Yo-jong would quickly step in, although the prospects for the country's long-term political future would be unclear.

Mr Kim’s health is of crucial importance because of worries that the serious illness or death of a leader venerated by many North Koreans could cause instability in the impoverished, nuclear-armed country.

The country’s aggressive military stance means a change of leadership or power struggle would also likely be of large concern to the likes of South Korea and the US.

While North Korea makes it virtually impossible for outsiders to discover what is happening at senior levels, South Korea’s main spy agency also has a mixed record on confirming developments in North Korea.

When Kim Jong-il died in December 2011, for instance, few outsiders knew it until it was reported by North Korea’s state media two days later.

On Sunday, North Korean state newspaper Rodong Sinmun reported that Mr Kim had sent his gratitude to workers who contributed to the construction of the city of Samjiyon.