"Given Mr. Newman's advanced age and health conditions, we urge [North Korea] to release Mr. Newman so he may return home and reunite with his family," White House spokesman Jay Carney said during a news briefing.
Newman, 85, has been held in North Korea since being removed from a plane Oct. 26 as he prepared to leave the country after a 10-day tourist visit. He and another retiree traveled with two Korean guides on a trip organized by a travel service in London.
The National Security Agency said Newman has a heart condition. Family members told media outlets they didn't know if he received his medication that was to be delivered by Swedish diplomats in Pyongyang.
North Korean officials say Newman confessed to espionage and war crimes. Newman's family said North Korea may have him confused with an American soldier with the same name, who earned a Silver Star during the Korean conflict.
"We are deeply concerned about the welfare of the U.S. citizens held in custody in [North Korea]," Carney said, noting Korean-American Kenneth Bae has been in North Korean custody for more than a year.
Bae, a Christian missionary arrested in November, was sentenced in May to 15 years of hard labor for "committing hostile acts" against the country.