Kim Hak Song, who was detained on Saturday, worked for Pyongyang University of Science and Technology, the North's KCNA news agency said.
The arrest of Kim Hak-Song means that the North now is holding four United States citizens, with the two countries at loggerheads over Pyongyang's nuclear and missile ambitions.
The other detainees are college student Otto Warmbier and Kim Dong-chul, a 63-year-old Korean-American.
The department will now work with the Swedish Embassy in Pyongyang, a result of the USA having no direct diplomatic relations with the North.
Such moves would be a step toward the country's goal of developing nuclear-armed missiles capable of reaching the USA mainland. The latter was arrested on charges of espionage.
In the statement Friday, the ministry said in response to the alleged plot on Kim Jong Un, a "Korean-style anti-terrorist attack will be commenced from this moment to sweep away the intelligence and plot-breeding organizations of the US imperialists and the puppet clique", referring to South Korea. DPRK is the acronym for the Democratic People's Republic of Korea.
"The relevant authority is now carrying out a detailed investigation into the crime of Kim Hak-song", KCNA said in a statement.
Two months later, Kim Dong Chul was sentenced to 10 years hard labor for subversion.
A State Department official in Washington today issued a terse comment about the American's reported detention.
Trump meets Abbas, predicts 'very good chance' of peace with Israel
On Tuesday, US Vice President Mike Pence said that "serious consideration" was still being given to the embassy move. Abbas assured Trump that Palestinians "are raising our youth, our children, our grandchildren on a culture of peace".
Now, at least two of the university's employees seem to be caught in the escalating tensions between the USA and North Korea.
On Wednesday, North Korea announced the detention of an accounting instructor at the same university, Kim Sang Duk - also known as Tony Kim - for "acts of hostility aimed at overthrowing the country".
While Trump told Bloomberg News on Monday that he would be "honored" to meet the North Korean dictator, many analysts believe that Kim no longer even aims to hold talks with the U.S.
Pyongyang also accused the CIA and South Korea's Intelligence Services of conspiring to assassinate leader Kim Jong-Un using "biochemical substances".
North Korea's announcement of the detainments comes amid tensions over fears that Pyongyang is preparing another round of nuclear or missile tests and comments.
"This is North Korea's hostage diplomacy", Dr. Koh said.
The Pyongyang University of Science and Technology (PUST) was founded by evangelical Christians and opened in 2010.
The United States has accused the North of using Warmbier as a political pawn.
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