The nuclear weapon that Iran sought to build in the early 2000s was based on designs that were both innovative and original, according to a new book that warns that Tehran’s scientists could produce a bomb quickly if they acquire the necessary fissile material and an order from the country’s leaders to do so.

Newly examined technical documents stolen from inside Iran in 2018 reveal that the country’s top-secret weapons program was preparing for a “cold test” of key components for a nuclear bomb by late 2003, and could have quickly progressed to true nuclear detonations.

Work on an Iranian nuclear weapon was halted in 2003, but by then Iran’s scientists had mastered nearly all the technical challenges of bombmaking and needed only a reliable source of fissile fuel — either enriched uranium or plutonium — authors David Albright and Sarah Burkhard write in “Iran’s Perilous Pursuit of Nuclear Weapons,” scheduled for publication next week. An advance copy of the book was provided to The Washington Post.

The release of the book comes amid intense diplomatic maneuvering in Vienna, as U.S. and Iranian officials negotiate reviving the 2015 Iran nuclear deal. Supporters of the agreement say the rekindled accord would put the brakes on Iran’s production of enriched uranium, which soared after President Donald Trump unilaterally withdrew from the pact three years ago. Critics note that Iran could quickly amass a bomb’s worth of fissile material after the deal’s key restrictions start to expire, beginning as early as 2025.

The book’s revelations are based on an analysis of a massive trove of nuclear documents smuggled out of a Tehran warehouse by Israeli operatives in 2018. Albright, founder of the Washington-based Institute for Science and International Security, was given access to hundreds of documents and photos, many of which are reproduced in the book.

Previous disclosures from the same cache of stolen documents have portrayed Iran as having been on the cusp of nuclear weapons capabilities by 2003, when Supreme Leader Ali Khamenei abruptly suspended the program. But the new book sheds light on the remarkable progress achieved by Iran’s “Amad Plan,” the secret effort to engineer and construct the Islamic Republic’s first nuclear weapon.

While U.S. intelligence agencies have long known that Iran received nuclear-related equipment and designs from Pakistani scientists in the 1980s and 1990s, Iran’s bomb design appears to be entirely indigenous, the authors say.

“This design was not a copy, but the product of a sophisticated nuclear weapons team, backed by sophisticated computer codes,” Albright and Burkhard write in the book. The Iranian documents portray a competent team of physicists and engineers nimbly making “refinements to the design, including additional miniaturization” of a warhead, they write.

The book credits a single scientist as being the Iranian nuclear maestro who ensured discipline and kept the project running: Mohsen Fakhrizadeh, a physicist and brigadier general, was the “undisputed leader” of Iran’s nuclear weapons program.

Fakhrizadeh was gunned down in Tehran last year as part of an assassination plot that Iranian officials have attributed to Israel’s Mossad spy agency. The book describes his killing as a “major blow,” while noting that the weapons-making expertise acquired under Fakhrizadeh still resides within Iran’s cadre of nuclear scientists and technicians.

“In the short to medium term, his loss may be felt the most during any nuclear breakout to build or test nuclear weapons,” Albright and Burkhard write.

Still, owing to Iran’s extensive, homegrown nuclear expertise, the country has essentially achieved an “on-demand” nuclear capability, allowing it to build a weapon quickly if it decides to, the authors argue.

“It would not take Iran long to build nuclear weapons today,” Albright said in an emailed summary provided to The Post. “With what Iran learned about building nuclear weapons during the Amad Plan — combined with its subsequent accomplishments — the Islamic Republic has developed a sophisticated capability to make nuclear weapons.”

Iran has denied seeking nuclear weapons and has alleged that at least some of the documents in the stolen trove are forgeries. But U.S. intelligence agencies have long believed that Iran operated a covert weapons program until 2003. The decision to suspend the effort followed revelations that Iran was building a secret uranium-enrichment plant near the city of Natanz. Another factor may have been the U.S. invasion of Iraq in March of that year.

The key question now, some analysts say, is how to best prevent Iran from acquiring weapons-grade uranium or plutonium.

“That remains the linchpin here: No nuclear weapon material, no weapon,” said Jon Wolfsthal, a former adviser to President Barack Obama on nonproliferation policy. “The know-how and technology to build a bomb is not as high a barrier to going nuclear as it once was, and the focus on weapon-usable material remains the right focus.”

Other experts noted that Iran still has not demonstrated the mastery of a few key technologies, such as the ability to integrate a nuclear warhead with a long-range delivery system.

“Iran would still need to develop the technical capability to be able to deliver such weapons by means of ballistic missiles,” said Daryl Kimball, executive director of the Arms Control Association.