Transcript for North Korea allegedly detains 4th US citizen

Terry Moran, thanks. To new tensions with north Korea where another U.S. Citizen being held there. Our chief global affairs correspondent Martha Raddatz has new details and, Martha, what do you know about this latest person that has been detained? Reporter: Good morning, robin. The North Korea news agency identified him as Kim hak-song, a teacher they say who worked for the Pyongyang university of science and technology. Last week the north Koreans announced an accounting instructor at the same university, Tony Kim had also been detained. The two other Americans are Kim dong chul and young university of Virginia student Otto wa Warmbier, some of the 800 to 1,000 Americans who visit every year. This comes as tensions are escalating over their nuclear -- not so-called, their nuclear ambitions and some are calling it a hostage diplomacy. Two reasons the north Koreans take hostage, bargaining chips and security and want to try to use them in negotiations but I think a bigger reason right now is they want to discourage the U.S. From taking any kind of military action which could threaten the lives of those hostages, it is one reason the U.S. So strongly warns American citizens not to visit north Korea. Robin. I think people are surprised about how many people -- Americans do travel there as you said. All right, Martha, thank you very much.

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