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.
Mr. Warmbier’s release came after a series of low-key communications between United States and North Korean officials in recent months, even as the North conducted missile tests and Washington hinted at the possibility of military action to stop the country’s advancing nuclear weapons program.
In Oslo last month, Joseph Y. Yun, the State Department’s point person on North Korea, met with Choe Son-hui of the North Korean Foreign Ministry, who handled relations with Washington, to push for the release of all four American citizens then being held in the North.
Then last week, North Korean diplomats at the United Nations told Mr. Yun that Mr. Warmbier had been in a coma for more than a year. The North later agreed to let Mr. Yun fly to Pyongyang to medically evacuate Mr. Warmbier.
The North told American officials that Mr. Warmbier contracted botulism and slipped into a coma after taking a sleeping pill. Doctors in Cincinnati have yet to comment on North Korea’s claim.
The North’s terse announcement on Thursday served to highlight many other unanswered questions about Mr. Warmbier, such as why North Korea kept his medical condition from United States officials for so long and why it decided to release him.
President Trump has defined his approach on North Korea as “maximum pressure and engagement.” He has repeatedly called on China, the North’s only major trading partner, to curtail economic ties with its neighbor to help rein in its nuclear pursuits. But Mr. Trump has also called North Korea’s leader, Kim Jong-un, a “pretty smart cookie” and said he would be “honored” to meet him under right circumstances.
If the North intended Mr. Warmbier’s release as a diplomatic overture toward Washington, whether it leads to broader talks would depend on Mr. Warmbier’s condition, analysts said.
“Otto is not in great shape right now,” his father, Fred Warmbier, told Fox News on Wednesday. “Otto has been terrorized and brutalized for 18 months by a pariah regime in North Korea.”
On Thursday, President Moon Jae-in of South Korea, who is scheduled to meet with Mr. Trump on June 29 and 30 in Washington to discuss a joint approach to the North, said that his government was willing to start unconditional talks with the North if it ceased further missile or nuclear tests.
In a speech marking the 17th anniversary of the 2000 summit meeting between the two Koreas, Mr. Moon urged the North to help promote peace on the divided Korean Peninsula by giving up its nuclear weapons program. He said South Korea would help North Korea rebuild its economy if it chose to denuclearize.
All of Mr. Moon’s predecessors in recent decades had made similar proposals, but Mr. Kim has only redoubled his efforts to build missiles capable of delivering nuclear warheads to the United States and its allies. Since taking office last month, Mr. Moon has vowed to play a more assertive role in resolving the North’s nuclear crisis through talks, saying that he was willing to meet with Mr. Kim if the circumstances were right.
There was no immediate response from the North to Mr. Moon’s speech on Thursday.
Mr. Warmbier was convicted on “anti-state” charges for trying to steal a propaganda poster from his hotel after arriving in Pyongyang on a tourist visa in January last year.
With Mr. Warmbier’s release, three American citizens are currently known to be held in North Korea, all of them Korean-Americans.
They include Kim Dong-chul, who was sentenced to 10 years’ hard labor on charges of spying and other offenses last year. North Korea has also detained Kim Hak-song and Tony Kim, also known as Kim Sang-duk, both Korean-American Christians, on unspecified charges in recent weeks.
In December, North Korea’s Supreme Court sentenced a South Korean-born Canadian pastor, the Rev. Lim Hyeon-soo, to hard labor for life on charges of carrying out “subversive plots” against North Korea.
At least six South Korean citizens, most of them Christian missionaries, have also been detained in North Korea on spying and other charges in recent years, officials in the South said.
The United States does not have diplomatic ties with North Korea. The Swedish Embassy in Pyongyang handles consular affairs for the Americans held there on Washington’s behalf. Reached by email, the Swedish ambassador, Torkel Stiernlöf, declined to comment on the conditions of the three Americans still in North Korean custody.