The pictures, released by state news agency KCNA last night, show the Supreme Leader cutting the ribbon at the opening of a fertiliser factory, with workers reportedly breaking into “thunderous cheers of hurrah”.

Claims carried in numerous media outlets last week suggested the 36-year-old had died after botched heart surgery, or was alternatively in a vegetative state.

Speculation was fuelled after he missed the birth anniversary celebrations of state founder Kim Il-sung, his grandfather, on April 15.

On the face of it, the pictures debunk the rumours about his demise.

However, journalist Roy Calley, author of Look With Your Eyes and Tell the World, an account of his numerous visits to the Hermit State as a tourist, is not convinced.

He told Express.co.uk: “Maybe I’m just being cynical but it does not look right to me.

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“I don’t think he smokes any more but he clearly has got lots of health issues.

“This is just another factory in PyongYang and it’s a really odd picture to release all of a sudden.

“There is simply no way to date it and the thing is, in the normal course of events, every day there is a picture released of the Supreme Leader opening something.”

Mr Calley, who believes Kim Yo-jong, Kim’s sister, would be the most likely candidate to succeed him, suggested the North Korean authorities could be playing for time while an internal power struggle plays itself out.

He explained: “When Kim’s father, Kim Jong-il, died, the North Korean public was not aware of it for three months.”

Kim’s appearance at the Sunchon fertiliser plant, which official media have claimed occurred on Friday, is a standard tactic of Kim’s whereby he presides over an event at a major industrial or social project, or at other times at military drills.

His second public visit this year to the site 30 miles north of Pyongyang featured a large group of officials from the army, the ruling Workers’ Party and the local community. Many wore face masks in an apparent precaution against the coronavirus, although Kim did not, and nor did either of the officials holding the ribbon.

Explaining the location, Koh Yu-hwan, the president of the Korea Institute for National Unification, a South Korean government think-tank, said: “Agricultural production is a top priority, which has a direct impact on the lives of the people.”

Koh said Kim’s sudden return was “a strategy to be in the centre of world news without resorting to nuclear or missile test”.

Asked about the reports, US President Donald Trump, who has met Kim on three occasions, said: “I’d rather not comment on it yet.”

“We’ll have something to say about it at the appropriate time.”