Yemeni officials say an American who worked as an English teacher in the Yemeni capital, Sanaa, has been detained on suspicions of espionage.

The officials told the Associated Press on Wednesday that he was arrested at his house in Sanaa on Tuesday and taken to the national security headquarters. Shiite rebels known as Houthis captured Sanaa in 2014, and are allied with security forces loyal to former President Ali Abdullah Saleh. It was not immediately clear if the American was being held by the Houthis or their allies.

The officials spoke on condition of anonymity because they were not authorized to speak to the press.

U.S. officials have declined to comment on the matter.