Speculation about the health of North Korean leader Kim Jong Il is intensifying after he failed to appear at celebrations marking the reclusive country's 60th birthday. Some reports suggest Mr Kim, who reportedly has chronic heart disease and diabetes, has suffered a stroke. North Korean officials have been forced to issue denials, claiming the reports are part of a "conspiracy plot". Senior North Korean diplomat Song Il Ho told Japan's Kyodo News that reports that the 66-year-old had fallen ill were "not true". The agency said North Korea's deputy leader and ceremonial head of state, Kim Yong Nam, said there is "no problem" with the supreme leader. Mr Kim, who has been rumoured to be in varying degrees of ill health for years, took over the reclusive state upon the death of his father 14 years ago in communism's first hereditary transfer of power. He attended the parade on the 50th and 55th anniversaries and was widely expected to do so this year as well. Since late 2002, North Korea has been locked in a stand-off with the United States over its nuclear ambitions. The country carried out its first nuclear test in 2006, but agreed last year to disable its nuclear facilities toward their ultimate dismantlement in exchange for economic aid and political concessions. The negotiations, however, hit a snag again recently with the two sides at odds over how to verify North Korea's accounting of its nuclear programs. Washington has delayed its promised removal of Pyongyang from the US "terrorism" blacklist.