Kenneth Bae, the Lynwood, Wash.-based American held in North Korea on account of “hostile acts” against the state, has been moved back to a labor camp there. Bae was arrested in November 2012 and was sentenced to 15 years of hard labor for planning to bring down the government through religious activities.

Bae used to lead tour groups in North Korea before he was accused of proselytizing and arrested in 2012. After he lost 50 pounds in prison, concern grew for his health, and he was shifted to a hospital from the labor camp, where he was farming vegetables from May 14 to Aug. 5 last year, his sister, Teri Chung, told Reuters. Chung learned from the U.S. state Department that Bae had been shifted back to the labor camp on Jan. 20, according to a CNN report.

"He's back to eight-hours-a-day, six-days-a-week hard labor," Chung told CNN. "We can't help but be concerned about that."

The 45 year-old Bae is a father to three children and suffers from diabetes, an enlarged heart, liver problems and back pain. Born in South Korea, he later immigrated to the U.S. with his parents and sister in 1985. After spending seven years in China as a Christian missionary, he started leading tour groups to a “special economic zone” created to encourage trade in northeastern North Korea.

State department spokeswoman Jen Psaki said, “The department of state has learned that the DPRK (North Korean authorities) transferred Mr. Bae from a hospital to a labor camp, a development with which we are deeply concerned. 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.”

There were previous efforts, such as those made by U.S. Presidents Bill Clinton and Jimmy Carter, to get him freed. North Korea recently released Merill E. Newman, an 85 year-old-war veteran, in December last year, after she was held while visiting the country as a tourist.

U.S. President Barrack Obama made a similar attempt at the annual National Prayer Breakfast on Thursday for Bae’s release and said, “We pray for Kenneth Bae, a Christian missionary who has been left in North Korea for 15 months. His family wants him home, and the United States will continue to do everything in our power to secure his release because Kenneth Bae deserves to be free."

Bae had turned down media reports and denied any ill-treatment at the press conference he gave on Jan. 20, but speculations are that he may have been speaking on strict editorial control, according to BBC. "I believe that my problem can be solved by close cooperation and agreement between the American government and the government of this country," Bae had said the press conference urging the U.S. government to help him and humbly apologizing to North Korea for his acts.

Psaki said that the Swedish embassy representatives have met Bae almost 10 times, with the most recent being Friday, Feb.7 in the labor camp. Late last month, she had also said that Washington is ready to send its human rights envoy for North Korea, Robert King to solve Bae's problem.