North Korean leader Kim Jong Un made his first reference to the execution of his powerful uncle in a New Year's address, saying the reclusive state's ruling party had become stronger after it was purged of "factional filth." And as he called for better relations with South Korea, he warned that another war on the Korean peninsula would cause a massive nuclear disaster that would hit the United States. Kim, the third generation of his family to rule North Korea, did not refer by name to his uncle Jang Song Thaek, who was executed last month in a rare public purge for crimes againstthe ruling Workers' Party and harming national interest. "Our party took a firm measure to get rid of factional filth that permeated the party," Kim said in a broadcast on state televsion that appeared to be pre-recorded, without showing if he was speaking to an audience. "Our unity strengthened hundredfold and party and revolutionary lines became more solid by purging the anti-party and anti-revolutionary faction," Kim said. After the sudden death of Kim's father in December 2011, Jang acted as regent to his young nephew as Kim establishedhimself in power. With the purge, Kim may have chosen to remove the only man who may have posed any real threat to him. Kim's call for improved ties with the South lacked any outline of steps to end the acrimony, and followed a threat from Pyongyang last month to strike Seoul without notice. "It is time to end abuse and slander that is only good for doing harm ... We will try hard to improve North-South ties," Kim said, adding that "dark clouds of nuclear war constantly hovered over the Korean peninsula". "If there ever is once again war on this land, it will bring about an enormous nuclear disaster and the United States will not be spared from it," he said. The two Koreas remain technically at war under a truce that ended the 1950-53 Korean War. The United States maintains 28 500 troops in South Korea in joint defence against the North. State media reported yesterday that Kim rode on a ski lift at the Masik ski resort, a widely publicised public project where the North expects up to 5 000 skiers a day when it opens this year. Kim has been pushing for massive projects throughout the country that go beyond the ski resort, pleasure parks and apartment blocks reported by state media, largely with the financial aid of its sole main ally China. Today, he emphasised his eagerness to pursue more construction projects. "This year, we should open up a new period of prosperity in construction. Construction is an important frontline to set grounds for the strong nation and people's happiness," he said.