Last month, Pyongyang detained Kim Sang Dok, a Pyongyang University accounting professor in his 50s it accused of "acts of hostility aimed to overturn" the regime of the North Korean leader, Kim Jong Un.
The North's army will launch "a series of more powerful anti-terrorism striking actions and mercilessly destroy the terrorists", read a report published by the state-run Korean Central News Agency on Monday. "A relevant institution is now conducting detailed investigation into his crimes", KCNA said. "We don't know what he is going to do", Song said.
Kim Hak-song had previously described himself as a Christian missionary who meant to start an experimental farm at PUST, Reuters news agency reported, citing an online post by Mr Kim. Pupils are generally children from the North's elite.
"We are aware of reports that a USA citizen was detained in North Korea", the statement said. DPRK is short for the Democratic People's Republic of Korea, North Korea's official name.
The arrest is the second of an American citizen by North Korea in two weeks.
Asked for comment on Trump's remarks that he would be "honored" to meet with the North's leader if circumstances are right, Rice said, "The president of the United States can't meet with Kim Jong-un, and certainly not under these circumstances".
Citing unidentified diplomatic sources, the Japanese newspaper wrote that in return for North Korea foreswearing its nuclear and missile technologies, the US promised it "would not seek regime change, regime collapse or an accelerated reunification of the Korean Peninsula, nor would it look for an excuse to advance north of the 38th parallel, the de facto inter-Korean border".
Both arrested are of Korean origin and had worked here as teachers.
On Friday, North Korea accused US and South Korean agents of plotting to kill its Supreme Leader, Kim Jong-un.
Here are the latest updates on the standoff between Kim Jong-un's regime and Donald Trump's administration. It is unclear what prompted his detention, but he has been charged with "hostile criminal acts with an aim to subvert the country".
But North Korea insists that it must continue to develop nuclear weapons because of the "hostile" policy of the United States.
The others are Otto Warmbier, serving a 15-year prison term with hard labor for alleged anti-state acts he allegedly tried to steal a propaganda banner at his tourist hotel and Kim Dong Chul, serving a 10-year term with hard labor for alleged espionage.
North Korea's announcement of the detainments comes as nations fear the isolated nation is preparing another round of nuclear or missile tests. The statement from the Foreign Ministry said a citizen named Kim had been paid $290,000 for himself and his "terrorist accomplices" as part of the plot.