“This situation is without precedent,” said Daryl Kimball, a nonproliferation expert with the Arms Control Assn., a Washington policy organization. “No country that has openly conducted test explosions and amassed a nuclear arsenal as North Korea has done has ever willingly eliminated its stockpile.”

U.S. intelligence agencies believe Pyongyang has assembled as many as 60 nuclear weapons and built a widely dispersed network of secret development and production facilities, some deep underground in the country’s rugged northern mountains, to create fissile material and testing components, and to assemble and store the actual warheads.

As part of any deal, U.S. officials also are likely to seek restrictions on North Korea’s ballistic missiles, especially those capable of hitting U.S. soil. Additional outside experts thus would be needed to inspect missile factories and test sites.

No matter how intrusive the inspections, there would be almost no way to guarantee North Korea wasn’t concealing a stash of components or a fully assembled warhead in case Kim or his successors faced a future threat to their survival, former officials and inspectors said.

“Say they declare 30 nukes. Can you verify 30? Yes,” said Robert Gallucci, who led 1994 talks with North Korea for the Clinton administration and is a professor at Georgetown University. “Can we ever, ever be certain they don’t have five other nukes somewhere? Absolutely not.”

If an accord with North Korea is struck, Pyongyang probably first would be required to submit a full accounting of its nuclear program — back to the beginning — to the International Atomic Energy Agency, the United Nations’ nuclear watchdog agency based in Vienna. That would be followed by comprehensive IAEA inspections aimed at confirming — or disproving — details in the documents.

Given the scale of Pyongyang’s program, the IAEA would need to hire and train a major new workforce and build or buy sophisticated monitoring equipment, from sensors to cameras, to ensure North Korea doesn’t cheat. The agency also would need the U.N. Security Council to approve the operation and fund it with a budget increase.

The IAEA said last year it had about 300 inspectors, including 80 who are working to monitor Iran’s 27 mostly dormant nuclear facilities as part of the 2015 nuclear accord that Trump abandoned last month. Iran and the other signatories are still honoring the agreement.

North Korea, by contrast, is believed to have up to 100 clandestine sites, according to a report by Rand Corp., a think tank based in Santa Monica. And Iran never built any nuclear weapons or intercontinental ballistic missiles.

Trump administration officials say their goal is complete, verifiable and irreversible disarmament, a high bar in a country that has pursued nuclear weapons for decades and on a far larger scale than Iran, Iraq, Libya and South Africa ever did. Those countries all gave up or were forced to give up their nuclear programs.

Any inspectors sent to North Korea would not be operating completely in the dark, however.

They presumably would have access to IAEA reports, satellite surveillance and intelligence from the U.S. and other countries about known and suspected nuclear facilities, identities of key scientists to interview, information from defectors, and even reports from experts allowed to visit key sites.

Siegfried Hecker, a former director of the nuclear weapons laboratory at Los Alamos, N.M., has toured North Korea’s major nuclear facilities four times and is the only U.S. scientist to visit its facility for enriching uranium, a bomb fuel. U.S. intelligence agencies had not spotted its construction.