Without explanation, North Korea abruptly canceled its invitation Friday for a U.S. special envoy to visit Pyongyang, bewildering American and South Korean officials who apparently expected the release this week of an American man detained there.

 At the invitation of the North, Ambassador Robert King, special envoy for North Korean human rights issues, had planned to travel to the communist nation on Friday in local time in an effort to free Kenneth Bae, a 45-year-old whose health is reportedly deteriorating.

 But the North informed the U.S. that it has withdrawn the invitation, according to the State Department. It did not provide a clear reason.

 "We are surprised and disappointed by North Korea's decision," Marie Harf, deputy spokeswoman for the department, said in a press release.

 "We have sought clarification from the Democratic People’s Republic of Korea 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," she added. "Ambassador King intends to return to Washington from Tokyo the afternoon of August 31."

 A U.S. government source said that Washington is still waiting for Pyongyang to allow King's trip.

 "Many people here are scratching their heads. Such a move by North Korea will only lead to a further loss of trust and credibility," the source said. "There is growing impatience here, with North Korea apparently playing a game with the life of an American citizen."

South Korean officials here also expressed dismay.

 "We expected Ambassador King's trip to North Korea and a resolution to the detention issue, which could help create a positive mood in easing tensions on the Korean Peninsula," a South Korean embassy official said. "We are surprised and disappointed."

 Speculation is rampant over why North Korea retracted the invitation just before King's travel there.

 Some observers said North Korea might be upset about the Obama administration's statement that it was not linking his trip with the possibility of resuming dialogue with Pyongyang.

 But the U.S. government source emphasized the North knew that the U.S. was separating the humanitarian matter with conditions for talks.

 Rather, North Korea may be trying to stage a war of nerves with the U.S. to gain concessions, said observers. (Yonhap)