North Korea advised the US State Department of its intention to test a nuclear device prior to today's underground explosion, but did not say when it would conduct the test, department spokeswoman Victoria Nuland told Reuters.
Nuland said the notice came through "usual channels" but declined to say when Washington received the notification.
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His mother Princess Diana was killed in a car crash in Paris in 1997 when he was just 12 and his brother William was 15.
The 21-year-old, who was arrested on Sunday, also allegedly injured two other people in the attack in the German city of Reutlingen.
She was going to the aid of a family member who got out of the car in the middle of the park and was dragged away by a different tiger.