The underground atomic test, the country's third since 2006, was conducted Tuesday over strong opposition from the international community, as it was in violation of U.N. Security Council sanctions. Kim Jong Un took over the leadership of the isolated Communist country in December 2011 after the death of his father, who had strongly promoted the nuclear program.
The North's official Korean Central News Agency carried pictures showing large crowds cheering the nuclear test at the rally Thursday.
South Korea's Yonhap News Agency reported the North Korean leader did not appear at the rally. Kim Ki-nam, a secretary of the ruling Workers' Party, addressed the crowd, saying the test was a result of a "resolute" decision by their leader, and described the event a "splendid national achievement" and a "stern and fair self-defense measure to cope with a hostile policy by the U.S. towards North Korea."
In a separate article, the KCNA said the Tuesday test had greatly encouraged North Koreans and quoted Cha Jong Chol, an officer of the Korean People's Army as saying, "The nuclear test is a self-defensive measure which is not contrary to any international law."
The article, referring the U.N. sanctions, said the "moves remind one of a new-born puppy knowing no fear of a tiger."
A KCNA commentary said the test involved a "smaller and lighter A-bomb," making it possible for the country to bolster up its physical deterrent.
Yonhap quoted South Korean nuclear scientists as saying they have not detected any radioisotopes from the North's nuclear test which would help determine the fissile material used in the test.
The scientists said the North's claim it used a "miniaturized" device may mean capability to make nuclear weapons small enough to fit on a missile.