SEOUL, South Korea — North Korea’s nuclear test Monday was driven by ailing Kim Jong Il’s plans to smooth the transition for his successor, and was a defiant signal to the United States that it considers itself an equal player in negotiations, experts said on Tuesday.

North Korea detonated a nuclear bomb underground and launched several short-range missiles Monday. After strong international rebuke, it tested two more short-range missiles on Tuesday.

"I think the internal dynamics are driving a lot of this," Daniel Pinkston, an international security expert with the International Crisis Group in Seoul, said of Monday’s launch.

North Korea is trying to regain the upper hand in talks with the U.S., and create a smooth transition for Kim Jong Il’s successor, by showing North Koreans "a remarkable achievement," said Kim Yong-hyun, a North Korean studies professor at Dongguk University.

He said the tests show Kim is still in firm control.

"The health problems he had last year were kind of a wake-up call," Pinkston said of Kim Jong Il reportedly having a stroke last summer.

David Garretson, a politics and economics professor for the University of Maryland University College Asia in South Korea, said the test was a political display to gain leverage by showing improved nuclear technology.

"It made the point that North Korea basically says, ‘You have to treat me as an equal, you have to treat us as a nuclear power,’ " said Garretson in a phone interview Tuesday from South Korea.

Stars and Stripes reporters Natasha Lee and Hwang Hae-rym contributed to this story.