SEOUL, South Korea — North Korea said on Thursday that it had freed the American college student Otto F. Warmbier on “humanitarian grounds” but did not reveal any details of his medical condition or the diplomatic negotiations that led to his release.

After he was held for more than a year in North Korea, Mr. Warmbier, 22, was flown from Pyongyang, the North Korean capital, to Ohio, his home state, in a coma on Tuesday. Mr. Warmbier has been in a coma since shortly after he was sentenced to 15 years of hard labor during a one-hour trial in March last year, according to his family members, who were briefed by American officials.

Doctors were evaluating Mr. Warmbier at the University of Cincinnati Medical Center, where he was admitted shortly after the plane carrying him landed in Cincinnati.

A one-sentence dispatch on Thursday by the North’s state-run Korean Central News Agency was the country’s first official comment on Mr. Warmbier since his release.