South Korea's domestic Yonhap news agency quoted North Korea's Central Radio as saying on Saturday that American pilots from a helicopter that landed in the North were being questioned.

``The report said relevant North Korean authorities were questioning the pilots of the downed helicopter to determine the background leading to the violation of the air space,'' Yonhap quoted the North Korean Central Radio as saying.

It also quoted an officer of the South Korea-U.S. combined forces command in Seoul as saying the two crewmen in the helicopter were believed to have escaped injury.

Both U.S. military officials and South Korean Defense Ministry officials in Seoul said they could not confirm the report.

An OH-58 helicopter, carrying a crew of two, was on a routine training orientation when contact was lost at about 11:30 a.m. Saturday (9:30 p.m. EST Friday).

North Korea's Central News Agency, monitored in Tokyo, said the helicopter was shot down.

Nagurka said Richardson arrived in Pyongyang Saturday evening local time and was informed of the helicopter incident by North Korean officials. ``Now this is at the top of his agenda,'' Nagurka said of Richardson, who had gone to the communist North to assess its relations with South Korea and to discuss a recent U.S.-North Korea nuclear pact.

North Korea has said it shot down the helicopter over its territory and the pilots were being questioned for intrusion, while the United States said they made an emergency landing.

Nagurka said Richardson, who was scheduled for a full day of meetings Sunday with North Korean officials before traveling to Seoul on Monday, had not seen the two pilots and could not confirm how their craft went down.

``He's made a number of requests, including a request to visit the (crash) site,'' Nagurka said. He said Richardson had advised the North Koreans of ``the utmost seriousness of this'' and the need to return the pilots quickly.

The United States is keeping the pressure on North Korea for information about two U.S. Army pilots whose helicopter was forced down after it crossed into that country's airspace.

A visiting congressman acting as a conduit between Washington and Pyongyang on the issue, cancelled scheduled discussions on a recent U.S.-North Korea nuclear pact to press for access to the detained pilots.

North Korea said it shot down the OH-58 reconnaissance helicopter and that the pilots were being questioned for intrusion.

The Defense Department said it was unclear whether the helicopter was shot down or made an emergency landing.

``We do not know at this time what exactly did take place,'' White House Chief of Staff Leon Panetta said on CNN's ``Evans & Novak'' program following Saturday's incident.

He conceded it was extremely unusual for a helicopter to stray over the border -- one of the world's most tense trouble spots for decades.

The Pentagon said the OH-58 was unarmed and on a routine training mission when it strayed over the border with South Korea and went down Saturday about three to four miles north of the demilitarized zone (DMZ) dividing North and South Korea.

Secretary of State Warren Christopher contacted the North Korean U.N. mission and U.S. officials had also talked with Democratic Representative Bill Richardson of New Mexico, who arrived in Pyongyang shortly after the incident for a previously scheduled visit, the Pentagon said.

A spokesman for Richardson, who is a personal friend of President Clinton, said the congressman had asked for ''immediate access'' to the two pilots and stressed that failure to return them ``would have a serious impact on U.S.-North Korean relations.''

Richardson cancelled all other discussions that were to have taken place on a recent U.S.-North Korea nuclear agreement, said Stu Nagurka, the congressman's spokesman.

Under the agreement signed in Geneva Oct. 21, meant to lessen fears the North was developing nuclear weapons, North Korea promised to halt its nuclear program and replace its graphite reactors with imported modern light-water models.

The United States says the fuel from the new reactors is virtually impossible to divert for bomb-making, unlike the old reactors which the CIA says have already produced enough plutonium for one or two weapons.

Panetta said he could not confirm that the helicopter was carrying reconnaissance equipment but said: ``Normally, helicopters along the DMZ are used for reconnaissance.''

He said it was ``obviously not'' normal for a U.S. helicopter to be over North Korea.

The Pentagon said that the pilots were on ``a routine training mission'' when they strayed into North Korean airspace and went down.

``We have indicated very serious concerns to the North Koreans about the welfare of these pilots. We want them returned,'' Panetta said.

The Pentagon identified the helicopter crew as Army Chief Warrant Officers David Hilemon of Clarksville, Tenn., and Bobby Hall of Brooksville, Fla.

The October nuclear agreement ended a two-year crisis over Pyongyang's alleged arms production plans that had led to threats of economic sanctions and warnings of possible military action.

North Korea keeps about 1 million men under arms, some 60 percent of them deployed near the border with the South. The United States has 37,000 troops in South Korea.