North Korea is marking the 101st anniversary of the birth of founding father Kim Il-sung as tensions continue over the country's nuclear programme. Leader Kim Jong-un visited the mausoleum of his grandfather and his father Kim Jong-il in Pyongyang, the official KCNA news agency reports. In recent weeks the North has threatened to attack South Korea, Japan and US bases in the region. The US has ruled out holding any more "artificial talks" with the North. "We cannot continue this charade and we cannot have a policy of rhetoric about denuclearisation. There have to be real steps here," Secretary of State John Kerry told the BBC after talks with leaders in Japan following a tour of East Asia. Mr Kerry said the North's main diplomatic ally, China, had made a very strong statement criticising Pyongyang for its recent behaviour. He said he hoped Beijing was now recognising the regional instability created by the actions of Kim Jong-un. Early on Monday Mr Kim was at the Kumsusan mausoleum to pay "high tribute and humblest reverence" to the country's former leaders, KCNA reports. The streets of Pyongyang are adorned with flags and banners for the holiday, a red-letter day for one of the world's most powerful cults of personality, says the BBC's John Sudworth in Seoul.