Bob King, the U.S. special envoy for North Korean human rights, was due to travel Friday from Tokyo to Pyongyang to request a pardon and amnesty for Kenneth Bae, and return the next day.
Bae, a 45-year-old tour operator and Christian missionary, was sentenced in April to 15 years of hard labor by the authoritarian state, which accused him of subversion. He was recently hospitalized.
Department spokeswoman Marie Harf said the U.S. was "surprised and disappointed by North Korea's decision" and remains gravely concerned about Bae's health.
U.S. officials said they were puzzled by the North Korean move, as the two sides had been coordinating closely to facilitate King's trip. It would have been the first public trip to North Korea by an Obama administration official in more than two years.
King intends to return to Washington from Tokyo on Saturday.
"We have sought clarification from the DPRK about its decision and have made every effort so that Ambassador King's trip could continue as planned or take place at a later date," Harf said in a statement, referring to the country's formal title of the Democratic People's Republic of Korea.
"We remain gravely concerned about Mr. Bae's health and we continue to urge the DPRK authorities to grant Mr. Bae special amnesty and immediate release on humanitarian grounds," Harf said.
The North Korean diplomatic mission at the United Nations in New York declined to comment Friday.
In a sign that all was not well, North Korea abruptly took a stronger tone Thursday in its criticism of U.S.-South Korean military drills that began Aug. 19 and were concluded Friday.
Pyongyang had initially responded to those computer-simulated drills with milder-than-usual language, which was seen as a sign of its interest in keeping up diplomacy. The regime of leader Kim Jong Un has also moved in recent weeks to improve relations with South Korea, a staunch U.S. ally.
"The trend for reconciliation and unity has faced a serious challenge due to the reckless nuclear war moves and confrontational racket against the DPRK being kicked up by the U.S. and the South Korean warmongers," the North's National Peace Committee of Korea said in Pyongyang's characteristic, combative style.
In the statement carried by the state-run news agency, the commission accused the U.S. of flying nuclear strategic bombers above South Korea this week in an attack drill.
North Korea has previously used detained Americans as bargaining chips in its standoff with the U.S. over its nuclear and missile programs. Multination aid-for-disarmament talks have been on hold since 2009, and efforts by Washington to negotiate a freeze in the North's nuclear program in exchange for food aid collapsed 18 months ago.
Bae is at least the sixth American detained in North Korea since 2009. The others were eventually allowed to leave without serving their terms, with some releases coming after prominent Americans, including former Presidents Bill Clinton and Jimmy Carter, visited North Korea.
Bae was arrested last November and accused of committing "hostile acts" against North Korea. He suffers from multiple health problems.
On Wednesday in Tokyo, King had cautioned that Washington had received no guarantees from Pyongyang that Bae would be freed.
Rep. Rick Larsen, who represents the Washington state district where Bae is from, expressed disappointment Friday about North Korea's "reverse course" and said it would be a difficult setback for Bae's family who were hoping for good news.
"The North Koreans gain nothing from this course reversal. It is time to let Kenneth come home to his family and get the medical attention he needs," Larsen said in a statement.
The last American to be detained by North Korea and then freed was Eddie Jun from California. The Korean-American was arrested for alleged unauthorized missionary work during several business trips to the country. He was brought back to the U.S. when King last visited Pyongyang in May 2011.
In August 2010, a State Department mission to free another detained American, Aijalon Gomes, ran into problems. A U.S. consular team was allowed to meet Gomes in Pyongyang but was not allowed to bring him home. He had been sentenced to eight years of hard labor for crossing into North Korea from China.
Two weeks later, former President Carter visited, and Gomes was released.
Associated Press writer Alexandra Olson at the United Nations contributed to this report.
