Senior U.S. intelligence officials are increasingly concerned that President-elect Donald Trump's threats to dismantle the Iran nuclear deal would bolster hard-liners in Tehran and spark a nuclear arms race in the Middle East.
Over the last month, U.S. intelligence analysts have written secret reports on the possible effects if the next administration abandoned or in effect sabotaged the arms control accord, as Trump has vowed to do during the campaign.
The concerns broke into the open Wednesday when CIA Director John Brennan issued a blunt public warning, saying it would be the "height of folly" and "disastrous" for Trump to scrub a deal that has blocked Iran's nuclear development.
Brennan told BBC TV that revoking the agreement could allow Iran to resume its now-halted nuclear program and spur other countries in the Middle East to develop or acquire nuclear weapons for protection.
"I think it would be disastrous" for Trump to jettison the deal, Brennan said.
"It could lead to a weapons program inside Iran that could lead other states in the region to embark on their own programs, so I think it would be height of folly if the next administration were to tear up that agreement," Brennan said.
He did not name other countries, but Saudi Arabia, Iran's staunch rival, is especially fearful of a nuclear-armed Iran given Tehran's aggressive pursuit of regional influence and power.
It is extremely rare for the CIA director to issue a public warning to an incoming administration, and it suggests deep concerns within the intelligence community about Trump's intentions.
Trump has delayed receiving more than a handful of in-depth intelligence briefings since election day, and it's unclear if he's been given the classified details of the Iran deal, including monitoring systems put in place to verify Iranian compliance.
Brennan suggested that the president-elect may be drawing his information from unreliable sources.
"There are a lot of people out there who read the papers and listened to news broadcasts where the facts may be a bit — you know — off," Brennan told the BBC.
"I want to make sure the new team understands what the reality is. It ultimately will be up to them to decide how to carry out their responsibilities," he said.
During the campaign, Trump variously promised to dismantle or revise the 2015 deal, which curbed Iran's ability to build or acquire nuclear weapons for at least a decade in exchange for an easing of sanctions on its trade, finances and oil industry.
Trump repeatedly described the accord as "a disaster" and suggested he would rip it up and "double up and triple up" sanctions on Iran.
Michael T. Flynn, Trump's pick for national security advisor, and Rep. Mike Pompeo (R-Kan.), Trump's choice to replace Brennan as CIA chief, have both been vocal critics as well.
"I look forward to rolling back this disastrous deal with the world's largest state sponsor of terrorism," Pompeo tweeted on Nov. 17.
Critics have complained that negotiations focused only on curbing Iran's nuclear program and not on Tehran's support for Hezbollah militias in Lebanon, Houthi rebels in Yemen and other issues of concern.
Proponents argued that stopping Iran from building a nuclear arsenal was the overriding priority and that U.S. sanctions remain on Iran's ballistic missile program and its support for terrorist groups.
The Iran deal apparently was a major topic when Trump met privately with President Obama for more than an hour at the White House two days after the election.
Obama told reporters later that imposing new U.S. sanctions on Iran while it remains in compliance would open a rift with the other major signatories to the deal — Britain, France, Germany, China and Russia.
He urged Trump and other Republican critics "to look at the facts because to unravel a deal that's working and preventing Iran from pursuing a nuclear weapon would be hard to explain, particularly if the alternative were to have them free from any obligations and go ahead and pursue a weapon."
Obama said "over a year of evidence" shows Iran has complied with the deal. He said that intelligence and military agencies in Israel, which opposed the deal, have also assessed that Iran has not violated its terms.
U.S. officials say Iran has reduced its stockpile of enriched uranium, placed most of its centrifuges in storage and disabled a reactor capable of producing plutonium as bomb fuel.
The International Atomic Energy Agency, the United Nations' nuclear watchdog agency, has found that Iran has exceeded a limit of so-called heavy water used in existing reactors. The violations were not major enough to trigger a renewal of sanctions under the deal.
"We are keeping a very close eye on what Iran is doing," Rep. Adam B. Schiff (D-Burbank), the top Democrat on the House Intelligence Committee, said in a telephone interview. "It is one of our top intelligence priorities."
If Trump backs out of the deal, Tehran would be able to restart its nuclear program "with very little the U.S. could do about it," Schiff said.
Robert M. Gates, a former CIA chief and secretary of Defense, has called for preserving the deal even though he said last year that the U.S. was "out-negotiated" by the Iranians.
"It would be a mistake to tear up the agreement at this point," Gates said Wednesday on "CBS This Morning." "I think we would be the ones isolated, not the Iranians, because none of our partners who helped to negotiate that would walk away from it. But I think what the new president can do is push back against the Iranians."