North Korea's leader Kim Jong-un was nowhere to be seen at the 69th anniversary celebrations of the founding of the Worker's Party of Korea, the party of his grandfather and North Korea's founder Kim Il-sung.

Mr Kim would normally pay tribute to his late grandfather, as well as his father, Kim Jong-il, at the event, which is held at the Kumsusan Palace of the Sun.

North Korea's state media usually chronicles Mr Kim's whereabouts in great detail, but has not made any mention of his activities since he attended a concert with his wife on September 3, fuelling rumours of a coup, or poor health.

A source close to North Korea's government said Mr Kim injured his leg and ankle while inspecting military exercises, but remains in firm control of the government.

"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 told Reuters.

Mr 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.

South Korea's unification ministry spokesman Lim Byeong-cheol said it believed Mr Kim remains in charge, citing a message conveyed by him via a visiting delegation last weekend.

"It appears it is being normally ruled by Kim Jong-un," he said.

South Korean defence minister Han Min-koo said the leader appears to be staying at a location north of Pyongyang, citing credible military intelligence for the information.

This is not Mr Kim's first absence from public view.

In June 2012, six months after coming to power, state media failed to report on or photograph him for 23 days.

Speculation that Mr Kim's unusually long absence from public view may be due to ill health was fuelled by a North Korean television report late last month that said he was suffering from "discomfort".

Some North Korea watchers also suggest that Mr Kim may have been sidelined in a power struggle, a scenario they say was reinforced by the unexpected visit on Saturday of a high-level delegation to the closing ceremony of the Asian Games in Incheon, South Korea.

ABC/Reuters