SEOUL, South Korea (AFP) — North Korea has detained another US citizen for committing “hostile acts,” it said Sunday, its second arrest of an American in a fortnight with tensions high between Pyongyang and Washington.

The arrest of Kim Hak-Song means that the North now is holding four US citizens, with the two countries at loggerheads over Pyongyang’s nuclear and missile ambitions.

Kim was detained on Saturday, the official Korean Central News Agency (KCNA) reported. “A relevant institution is now conducting detailed investigation into his crimes,” it added.The two-paragraph report gave no further details of the latest arrest.But it said Kim had been working for the Pyongyang University of Science and Technology (PUST) — an institution founded by evangelical Christians from overseas and opened in 2010, which is known to have a number of American faculty members. Pupils are generally children from the North’s elite.A State Department official in Washington on Sunday issued a terse comment about the American’s reported detention.”We are aware of reports that a US citizen was detained in North Korea,” the statement said.”The security of US citizens is one of the Department’s highest priorities. When a US citizen is reported to be detained in North Korea, we work with the Swedish Embassy in Pyongyang, which serves as the United States’ Protecting Power in North Korea,” the State Department official said, adding that no additional comment was being offered “due to privacy considerations.”Kim is the second of the university’s personnel to have been detained in as many weeks.Accounting professor Kim Sang-Duk, or Tony Kim, also a US citizen, was held on April 22, the North confirmed last week, for trying to “overturn” the regime.He was detained at the capital’s airport as he tried to leave the country after teaching for several weeks at the university.KCNA said he had been held for “committing criminal acts of hostility aimed to overturn the DPRK,” using an abbreviation for the country’s official name.Using similar phrasing to Sunday’s dispatch, it added that Kim was “under detention by a relevant law enforcement body which is conducting detailed investigation into his crimes.”PUST officials could not immediately be reached for comment in connection with Saturday’s arrest.In a statement in late April the university said Tony Kim’s arrest was “not connected in any way with the work of PUST.”