Gordan Chang: Kim Jong Un wants to embarrass Obama

A source tells CNN an American has been detained in North Korea.

We've learned that the man, identified as Miller Matthew Todd, was taken into custody on April 10th.

A western diplomat tells CNN the 24-year-old tore up his visa at customs and appeared to go willingly with the North Koreans.

North Korea says it has American in custody

This comes as South Korea says the North may be preparing a nuclear weapons test, adding that it has completed all of the preliminary steps required to conduct such a test.

Possible North Korean nuclear test looms over Obama's visit to South Korea

The timing comes as President Obama is visiting South Korea Friday, a trip North Korea has condemned.

Gordon Chang,  author of "Nuclear Showdown: North Korea Takes on the World" is OutFront to break down what this latest news means.