The North Korean leader, Kim Jong-un, has appeared in public for the first time in almost three weeks, The Guardian reports citing state media, following speculation that he had been seriously ill following heart surgery.

The state news agency KCNA released photographs purportedly showing Kim opening a fertilizer plant in Sunchon, north of the capital Pyongyang.

KCNA said Kim, accompanied by other senior officials, including his influential younger sister, Kim Yo-jong, cut a ribbon at a ceremony on Friday.

What appeared to be thousands of people attending the event, many of them wearing face masks, released balloons and “broke into thunderous cheers of ‘hurrah!’ for the Supreme Leader,” the agency said.

The images showed Kim smiling and talking to aides, as well as touring the plant. The authenticity of the photos, published on the website of the official Rodong Sinmun newspaper, could not be immediately verified.

The North Korean leader was last seen in public on April 11 when he presided over a Workers’ party politburo meeting. State media did published a single photograph of Kim for well over two weeks after that date, but carried reports of his daily routine, including diplomatic messages sent to other world leaders.

Speculation over his whereabouts gathered pace after he missed the April 15 commemoration of the birthday of his grandfather – and North Korea’s founder, Kim Il-sung – which is the most important event in the country’s political calendar. It was the first time the younger Kim had missed the event since becoming leader.