Seoul, July 30 (DPA) North Korean leader Kim Jong Il is receiving dialysis treatment due to his chronic renal failure, a North Korean watcher said Thursday here.

Ha Tae Gyung -- who runs South Korea-based Open Radio for North Korea, which broadcasts into the totalitarian state -- said Kim's treatments began before his country conducted a nuclear test May 25.

Ha said he received the information from multiple sources in North Korea who he did not name.

Kim's health is a closely guarded secret in North Korea, but he is believed to suffer from diabetes and heart disease and South Korean intelligence said he had a stroke in August.

His health is closely watched internationally because Kim, 67, has not publicly named a successor. Some North Korea watchers said, however, that his third and youngest son, Jong Un, who is in his mid-20s, is being groomed to take over from his father.

Observers said Kim's worsening health and his wish to be succeeded by his son prompted him, in a show of strength, to conduct the nuclear test, North Korea's second after an initial one in 2006, as well as a series of missile launches, including a long-range rocket in April - all of which were internationally condemned.