North Korea on Sunday said it had detained a US citizen who worked with the Pyongyang University of Science and Technology on suspicion of carrying out “hostile acts” against the regime. Kim Hak-song was taken into custody on May 6, according to the state-run KCNA news agency.

While other details are largely unavailable, it is believe that Kim Hak-song was conducting some business with the university and was being investigated by a “relevant authority”. Officials in Washington DC told both CNN and the BBC that they were of the reports of his detention.

The university is largely funded by Christian charities in the United States and South Korea, and is considered an elite institution. A former professor at the university, Kim Sang-duck, is among three other US citizens currently being detained in the isolated country. The university’s chancellor Park Chan-mo had said that Kim Sang-duck had been trying to flee the country when he was caught on April 24.

The detention comes as tensions between North Korea and the US have been escalatingIn April 2016, Kim Dong-chul was sentenced to 10 years’ of hard labour for espionage. He was arrested in October 2015. In January 2016, a 21-year-old student, Otto Warmbier, was arrested for trying to steal a propaganda banner. He was also sentenced to 15 years’ of hard labour. The US has accused North Korea of detaining its citizens to use them as pawns