Kim Jong Un
She said she believed the arrest was leader Kim Jong Un "trying to really show his strength to the people of North Korea."
Seoul has said it will not let its guard down and is watching the situation closely.
Both are thin-skinned leaders with huge egos and a preference for maximalist solutions. That could lead to devastating consequences.
Earlier speculation suggested it may have had something to do with marking the birthday of the deceased founder of the country.
North Korea celebrates its founder's birthday on Saturday and has tested missiles on significant occasions in the past.
Former North Korean ambassador to the U.K. Thae Yong Ho said Kim Jong Un was ready to defend his government at all costs, including by nuclear force.
The Seoul branch of the U.N. Human Rights Committee employs six people to listen to defectors' accounts of human rights abuses.
A North Korean spokesperson said the North would push forward with its nuclear plans.
China said that international action should wait until the investigation is complete.
A man claiming to be Kim Han Sol released a video saying that he is in hiding with his mother and sister.
Pyongyang's latest missile launches and the assassination of Kim Jong Un's estranged half-brother have added urgency, driving home the need for Washington to confront the security challenge.
Malaysian police investigating the murder of Kim Jong Nam questioned up to three men hiding in the North Korean embassy.
Relations have deteriorated since the assassination of Kim Jong Nam in Kuala Lumpur.
Kim Jong Un’s reign has been one of “terror”, say South Korean Intelligence Service.
Diplomat is one of eight Koreans under investigation after apparent assassination of Kim Jong Nam.
The announcement comes after an attempted break-in at the morgue where Kim Jong Nam is being held.
The ambassador's statement casts the manners of North Korea into question