Washington (CNN) North Korea quietly reached out to U.S. officials through the United Nations in New York last fall to propose formal peace talks on ending the Korean War, a response to President Barack Obama's comments that the U.S. was willing to engage Pyongyang as it has with other rogue regimes, senior U.S. officials told CNN.

That effort fell short, the officials said, with the North Koreans refusing to include their nuclear program in any negotiations as the U.S. required and soon after testing a nuclear weapon.

But it represented a new step from the Obama administration as it tried to lure the hermetic country out of its isolation and extend its track record of successful negotiations with nations long at odds with the United States, such as Iran and Cuba.

The U.S. told North Korea it was willing to discuss a formal peace to replace the 63-year-old armistice that ended hostilities after the Korean War, but only if efforts to curb Pyongyang's nuclear program were part of the discussions.

In doing so, the administration dropped a longstanding demand that North Korea take steps toward "denuclearization" before talks on a formal peace treaty began. Still, the North Koreans refused to allow the nuclear issue to be part of any talks.

"It's a tweaking of the conditions," said Bruce Klingner, a senior fellow at the Heritage Foundation and former deputy division chief for the CIA in South Korea, describing the administration's move.

"Rather than requiring progress on denuclearization before negotiations, it seems the administration agreed to the idea of peace talks but required denuclearization talks to be included," Klingner said.

The Wall Street Journal first reported on the diplomatic exchanges, but the Obama administration disputed their depiction of events, saying it was North Korea that first proposed the talks rather than the United States, which maintained its focus on ridding the Korean Peninsula of nuclear weapons.

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"To be clear, it was the North Koreans who proposed discussing a peace treaty," State Department spokesman John Kirby said in a statement. "We carefully considered their proposal, and made clear that denuclearization had to be part of any such discussion. The North rejected our response."

North Korea has regularly proposed peace talks over the years, pushing the U.S. to replace the 1953 armistice with a formal peace treaty, said Klingner.

"They periodically raise the idea and it never really gets far," he said.

One issue that complicates the effort is the need to establish parameters for any negotiations before they begin, in particular to ensure that North Korea's conventional threat to the South is defused before there's any demand to remove some of the 28,500 U.S. troops in South Korea.

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Those soldiers, airmen and Marines provide some deterrent to the North, a highly militarized country that maintains a standing army of 1.2 million active soldiers, 70% of whom are deployed within 100 miles of the border with South Korea, according to Klingner.

A peace treaty should only be signed after arduous negotiations to reduce the North Korean conventional force threat to South Korea, said Klingner, who has taken part in other treaty negotiations.

"You also have to implement confidence-building measures as the U.S. did in Europe," Klingner said, mentioning steps like advance notice of large-scale military exercises and reducing the number of North Korean forces near the demilitarized zone dividing the two Koreas.

The U.S. attempt to reach out ended definitively with North Korea's January 6 announcement that it had tested a hydrogen bomb, following nuclear weapons tests in 2006, 2009 and 2013.

Though the U.S. has expressed doubt that a hydrogen bomb was indeed tested -- with some officials instead characterizing the explosion as having perhaps contained components of such a weapon -- the U.S. responded last week with a new round of sanctions against Pyongyang.

Photos: North Korea launches rocket Photos: North Korea launches rocket The Kwangmyongsong carrier rocket blasted off from the Sohae launch facility at 9 a.m Sunday (7:30 p.m. ET Saturday), entering orbit nine minutes and 46 seconds after liftoff, North Korea's state news agency KCNA reported. Hide Caption 1 of 8 Photos: North Korea launches rocket A state TV newsreader said the operation had been personally ordered and directed by North Korean leader Kim Jong Un. Hide Caption 2 of 8 Photos: North Korea launches rocket State media reported that more satellite launches were planned. Hide Caption 3 of 8 Photos: North Korea launches rocket U.N. Secretary-General Ban Ki-moon called the launch "deeply deplorable" and in violation of Security Council resolutions "despite the united plea of the international community against such an act. Hide Caption 4 of 8 Photos: North Korea launches rocket North Korean leader Kim Jong Un looked on as the rocket blasted off. Hide Caption 5 of 8 Photos: North Korea launches rocket State media captures a moment on the rocket at lift off. Hide Caption 6 of 8 Photos: North Korea launches rocket The United States, South Korea, Japan, China, Russia, Britain and France, as well as the European Union and NATO, were swift to condemn the action. Hide Caption 7 of 8 Photos: North Korea launches rocket An official photograph shows the control room. Hide Caption 8 of 8

The measures freeze the assets of anyone doing business related to North Korea's nuclear weapons programs or involved in human rights violations there.

The latest diplomatic dance between the U.S. and North Korea started in October, when Obama signaled that Washington was willing to negotiate a deal similar to the agreement reached last year with Iran, in which Tehran agreed to significantly curb its nuclear program in exchange for international sanctions being lifted.

"As my administration has shown with Iran and with Cuba, we are also prepared to engage nations with which we've had troubled histories," Obama said in an October 16 press conference alongside South Korean President Park Geun-hye.

"At the point where Pyongyang says, 'We're interested in seeing relief from sanctions and improved relations, and we are prepared to have a serious conversation about denuclearization,' I think it's fair to say we'll be right there at the table," he added.

The Obama administration at that time said it would waive the standard requirement that North Korea make progress on denuclearization before peace talks could begin, but said denuclearization had to remain on the table.

Park said South Korea was also ready to engage with Pyongyang if the regime showed it was serious about curtailing its nuclear arsenal.

"Should North Korea demonstrate a genuine willingness towards denuclearization, we reaffirm that Korea and the U.S., along with the rest of the international community, stand ready to extend cooperative measures to the North," she said.

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A day later, North Korea rejected the idea of resuming international talks on ending its nuclear program and suggested instead that the United States negotiate a formal peace treaty to end the Korean War. Within weeks, senior administration officials said, the regime repeated the message thorough its mission to the United Nations.

In an October 17 statement published by the state-controlled Korea Central News Agency and read in part on state-run television KRT, the North Korean Foreign Ministry said past efforts to focus exclusively on international denuclearization talks had failed.

The statement said that increased diplomatic pressure and sanctions wouldn't bring North Korea to the negotiating table, but that a peace treaty could reduce tensions and make it possible to "finally put an end to the nuclear arms race."

"No issue in which the countries concerned, including the U.S., are interested can be settled unless a peace treaty is concluded before anything else," the statement said. "If the United States insists on taking a different path, the Korean peninsula will only see our unlimited nuclear deterrent being strengthened further."