Kenneth Bae, an American who has been detained in North Korea for 15 months, has been sent back to a labor camp, the U.S. State Department said on Friday.

Bae was arrested in 2012 for leading tour groups in North Korea and sentenced to 15 years of hard labor for reasons that the U.S. has yet to determine. Bae was taken to a hospital in the summer of 2013 for health problems. His sister, Terri Chung, said on Jan. 20 that the State Department told her that Bae was being returned to a labor camp, but the The State Department did not publicly confirm that information until today.

“The Department of State has learned that the DPRK transferred Mr. Bae from a hospital to a labor camp, a development with which we are deeply concerned,” State Department Spokesperson Jen Psaki said. “We also remain gravely concerned about Mr. Bae’s health, and we continue to urge DPRK authorities to grant Mr. Bae special amnesty and immediate release on humanitarian grounds.”

Psaki added that Bae has had access to representatives from the Swedish Embassy during his incarceration: “Swedish Embassy representatives have met with Mr. Bae ten times since his detention, most recently on February 7 in a labor camp.”