This file picture taken by North Korea's official Korean Central News Agency on October 10, 2013 shows North Korean leader Kim Jong Un, accompanied by senior army officials, visiting the Kumsusan Palace in Pyongyang to pay tribute to late leaders Kim Il Sung and Kim Jong Il on the occasion of the 68th anniversary of the Workers' Party of Korea (WPK). Kim apparently missed a key political anniversary event on Friday, extending a month-long absence that has fuelled rampant speculation about his physical health and political future.

Reuters/Beijing/Seoul

North Korean leader Kim Jong Un is in firm control of his government but hurt his leg taking part in a military drill, a source with access to the secretive North's leadership said, playing down speculation over the 31-year-old's health and grip on power in the nuclear-capable nation.

North Korea's state media, which usually chronicle Kim's activities in great detail, have not mentioned any public appearances since he attended a concert with his wife on September 3 and the official KCNA news agency indicated he did not attend an important political anniversary on Friday.

In the previous two years, Kim marked the anniversary of the founding of North Korea's Workers' Party with a post-midnight visit to the Pyongyang mausoleum where the bodies of his father and grandfather are interred.

But the report by KCNA did not mention Kim's name in a list of high-level party and military officials who attended an event at the mausoleum on Friday. A flower basket from Kim was placed at the mausoleum, it said.

The source with access to the North's leadership, who has close ties to Pyongyang and Beijing, said on Thursday that Kim had hurt his leg while inspecting military exercises.

"He ordered all the generals to take part in drills and he took part too. They were crawling and running and rolling around, and he pulled a tendon," the source told Reuters on condition of anonymity.

"He injured his ankle and knee around late August or early September while drilling because he is overweight. He limped around in the beginning but the injury worsened," the source said.

Kim, who has rapidly gained weight since coming to power after his father died of a heart attack in 2011, had been seen walking with a limp since an event with important officials in July, which would imply he may have aggravated an earlier injury.

Kim needs about 100 days to recuperate, said the source, whose information could not be independently verified.

"Kim Jong Un is in total control," said the source.

Kim's absence from public view is fuelling speculation over the state of his health and whether he may have been sidelined in a power struggle.

On Friday, South Korea's Unification Ministry said it believes Kim remains in charge, citing a message conveyed by him via a delegation visiting last weekend, and Pyongyang's continued public position that Kim leads the country.