SEOUL, SOUTH KOREA - North Korea's leader Kim Jong-Il is undergoing kidney dialysis twice a week as a result of his diabetes, a South Korean activist said Thursday, quoting unidentified sources in Pyongyang.

The health of Kim, 67, is the subject of intense interest as he has not formally named someone to succeed him at the helm of the secretive communist state.

'His illness suddenly became worse last May, forcing him to receive dialysis,' Ha Tae-Keung, president of the Open Radio for North Korea, said on a radio talk show.

'The nuclear test was carried out in order to prevent Kim's health problems from sparking rifts among power elites,' added Ha, whose Seoul-based organisation broadcasts programmes to the North.

Kim, who has a history of diabetes and heart disease, is widely believed to have suffered a stroke in August last year.

In video footage recorded in March and shown on North Korean state television last week, Kim barely used his left hand. Most still photos released since his reported stroke have not shown him using his left hand.

North Korea launched a long-range rocket on April 5 and conducted a nuclear test on May 25, its second following the first in 2006. It also has fired several short-range missiles and renounced the truce on the Korean peninsula.

US and South Korean officials believe the ailing Kim was staging a show of strength to bolster his authority as he tries to put in place a succession plan involving his youngest son, 26-year-old Jong-Un.

According to reports, North Koreans are being taught new songs aimed at bolstering loyalty to the next leader, addressing Jong-Un as 'General Kim.'