North Korea insisted Tuesday that U.S. officials apologize for the intrusion of an American helicopter into its airspace, which it called a deliberate act of espionage.

U.S. officials again denied that the helicopter was spying and insisted it crossed the border accidentally. The State Department dispatched an envoy Monday to seek the release of the surviving pilot, Bobby Hall, but prospects for his freedom dimmed with North Korea's latest pronouncement.The statement by the North's official Korean Central News Agency was only its third mention of the Dec. 17 incident, in which the U.S. Army OH-58C helicopter crossed into North Korea and crashed or was shot down.

Hall was captured and his co-pilot, Chief Warrant Officer David Hilemon, died. Hilemon's body was returned Thursday.

The North Korean statement Tuesday came just as there had appeared to be progress in obtaining Hall's release. The statement raised questions whether the Pyongyang government is trying to obtain concessions from the United States and whether military hard-liners are in control in the reclusive communist country.

"All facts clearly prove that the intrusion of the U.S. helicopter . . . is a grave violation of the sovereignty of the DPRK (Democratic People's Republic of Korea) and a deliberate act for espionage on it," the news agency's statement said.

North Korea has said Hall will not be released until it completes its investigation. Its statement Tuesday said Washington "must admit its responsibility . . . and clearly show an honest and reasonable attitude before it is too late."

South Korea's Hankyoreh Shinmun newspaper reported in Wednesday's editions, seen in Seoul late Tuesday, that the investigation is being held up by Hall's refusal to cooperate.

"If Warrant Officer Hall does not tell the truth and continues to be uncooperative, the investigation will take a considerably long time," the newspaper quoted a senior North Korean diplomat at the United Nations as saying.

The pilot apparently has only provided his name, rank and unit, the newspaper said.

Jim Coles, a spokesman for the U.S. and U.N. military presence in Korea, adamantly denied North Korea's accusations of espionage.

"As we have said, this was a routine training flight that unfortunately strayed into DPRK airspace," he said Tuesday.

Korean News Service, a pro-North Korean news agency in Tokyo, released a photograph Tuesday from the North Korean government that the agency said showed Hall just after he was taken captive. He is standing in a wooded area with his arms in the air, wearing a flight jumpsuit and apparently unhurt.

U.S. officials have said the pilots may have been disoriented because fresh heavy snow had covered landmarks and navigational markers.

North Korea rejected that explanation. It said the helicopter was flying at a low altitude of 1,200 feet when it crossed the rugged zone separating the two Koreas at 10:35 a.m., the KCNA statement said.

After two warning signals, the helicopter lowered its altitude and continued to fly north, it said. Anti-aircraft gunners opened fire at 10:45 a.m. Hit by one shot, the helicopter "fell aflame to a ravine," it said.

North Korea said "the fact that the helicopter did not respond to our warning signals but tried to escape . . . eloquently proves that the intrusion was not a `stray' flight.' "