N. Korean leader Kim not believed to be critically ill: source

North Korean leader Kim Jong Un is not believed to be critically ill, an official with the Chinese Communist Party's International Liaison Department told Reuters on Tuesday, following media reports about the state of Kim's health.

The official declined to be identified given the sensitivity of the matter. The International Liaison Department is the main Chinese body dealing with neighbouring North Korea.

North Korean leader Kim Jong Un is receiving treatment after undergoing a cardiovascular procedure early this month, a South Korean media report said, amid speculation over Kim's health following his absence from a key anniversary event.

North Korea marked the anniversary of the birthday of its founding father and Kim's grandfather, Kim Il Sung, as a national holiday on April 15, but Kim was not seen in attendance.

Daily NK, a speciality website run mostly by North Korean defectors, cited unidentified sources inside the isolated state saying Kim is recovering at a villa in the Mount Kumgang resort county of Hyangsan on the east coast after getting the procedure on April 12 at a hospital there.

Reporting from inside North Korea is notoriously difficult, especially on matters concerning the country's leadership, given tight controls on information.

South Korea's Unification Ministry, which handles inter-Korean affairs, declined to comment on the report.

Kim's health has deteriorated in recent months due to heavy smoking, obesity and overwork, the Daily NK report said.

"My understanding is that he had been struggling (with cardiovascular problems) since last August but it worsened after repeated visits to Mount Paektu," a source was quoted as saying, referring to the country's sacred mountain.

Kim left for the hospital after presiding over a meeting of the ruling Workers' Party's politburo on April 11, where Kim was publicly last seen, the report said.

Pyongyang fired multiple short-range missiles last week which Seoul officials said were also part of the Kim Il Sung birthday celebration. Such military events would usually be observed by Kim, but there was no KCNA report on the test at all.