Pyongyang: North Korean leader Kim Jong Un said the country would not use a nuclear weapon unless its sovereignty is encroached by "invasive hostile forces with nuclear weapons," according to the country's state news agency KCNA. He made the remarks Saturday at the ruling Workers' Party of Korea's Seventh Congress in Pyongyang, which began the day before. Kim also reportedly said North Korea will faithfully fulfil its nuclear nonproliferation obligations and make an effort to realize global denuclearisation. In his 15-minute opening speech on Friday, Kim touted the country's weapons development, saying they had "elevated our respect to the world and enemies." In January, Pyongyang announced that it had successfully tested a thermonuclear device, which, if true, would mark a significant advance in its nuclear capabilities. It has since made a number of public demonstrations of its nuclear program's advancement, including rocket and submarine-based missile tests. It also announced it had miniaturized a warhead in early March. Kim called on the country to push forward "the building of nuclear force and boost self-defensive nuclear force both in quality and quantity," according to KCNA. Kim also said that the congress would review the party's "brilliant successes" and put together tasks to "keep ushering in a great golden age of socialist construction." The country's provocative nuclear stance has triggered some of the harshest UN sanctions imposed against North Korea and irritated his most powerful ally, China. The sole remaining symbol of cooperation with South Korea -- the Kaesong Industrial Complex near the demilitarized zone -- has also shut down during his tenure. Details of the gathering had been kept secret from the foreign press and the North Korean public until a Friday evening news bulletin. The previous one, in 1980, marked the naming of Kim's father, Kim Jong Il, as successor to his own father, North Korea's founder Kim Il Sung, as leader of the reclusive nation.