SEOUL, South Korea — Long columns of goose-stepping soldiers, accompanied by what North Korea claimed were nuclear-tipped missiles, marched through central Pyongyang, the capital, on Saturday, as the country’s leader, Kim Jong-un, gave his first public speech in three years to emphasize his “love for the people” and declare his readiness to “fight any form of war” with the United States.

Mr. Kim celebrated the 70th anniversary of his ruling Workers’ Party on Saturday with what appeared to be one of the largest military parades the North had ever organized. As warplanes flew overhead, the plaza in Pyongyang was filled with soldiers and citizens chanting slogans of loyalty to the Kim family and waving pink and red artificial flowers in synchronized moves.

In a 25-minute speech before the parade, Mr. Kim spoke of his “love” and “dedication to the people,” whom he thanked for staying with his party through decades of American-led economic sanctions and blockades.