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.”