A US Air Force officer has defected to Iran and shared information that could cause "serious damage" to America's national security, officials have revealed.

The former Air Force intelligence specialist was charged with espionage and was accused of working for Iran, according to an unsealed federal indictment.

The announcement arrived after Assistant Attorney General for National Security John Demers and other senior officials held a call with reporters to discuss what they called “a national security related action involving Iran”.

Mr Demers was joined by US Attorney for Washington, Jessie Liu, FBI Executive Assistant Director for National Security Jay Tabb, Treasury Department director of Foreign Assets Control Adrea Gacki and Air Force Office of Special Investigations Special Agent Terry Phillips.

The officials discussed the unsealed indictment against Monica Witt, a former counterintelligence officer for the Air Force Office of Special Investigations. Ms Witt defected to Iran nearly six years ago in 2013.

Also charged are four Iranian hackers. Prosecutors say they targeted former colleagues of Ms Witt’s in the intelligence community.

The indictment says the four Iranians were acting on behalf of the government-linked Iranian Revolutionary Guard Corps.

“It is a sad day for America when one of its citizens betrays our country,” Mr Demers, the head of the Justice Department’s national security division, said on the call.

Ms Witt remains at-large. The 39-year-old “has been indicted by a federal grand jury in the District of Columbia for conspiracy to deliver and delivering national defence information to representatives of the Iranian government,” according to the indictment that was unsealed on Wednesday morning.

“Witt, who defected to Iran in 2013, is alleged to have assisted Iranian intelligence services in targeting her former fellow agents in the US Intelligence Community (USIC). Witt is also alleged to have disclosed the code name and classified mission of a US Department of Defence Special Access Program,” the indictment continues.

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A warrant has been placed for her arrest.

Monica Elfriede Witt is #wanted by the #FBI for her alleged involvement in criminal activities to include espionage & conspiracy to commit espionage. If you have info concerning Witt, contact your local FBI office or the nearest U.S. Embassy or Consulate. https://t.co/f0OsA1hayy pic.twitter.com/eb4pe5UsEe — FBI (@FBI) February 13, 2019

The four hackers, whose names are Mojtaba Masoumpour, Behzad Mesri, Hossein Parvar and Mohamad Paryar, have also been charged with conspiracy, attempts to commit computer intrusion and aggravated identity theft. Their alleged crimes date back to 2014 through 2015, in which they are charged with “using fictional and imposter social media accounts and working on behalf of the Iranian Revolutionary Guard Corps (IRGC), sought to deploy malware that would provide them covert access to the targets’ computers and networks.”

The hackers, referred to in the indictment as “Cyber Conspirators,” also remain at-large and have warrants placed for each other their arrests.

US Treasury Secretary Steven Mnuchin said the agency was “taking action against “malicious Iranian cyber actors and covert operations that have targeted Americans at home and overseas as part of our ongoing efforts to counter the Iranian regime’s cyber-attacks.”

“Treasury is sanctioning New Horizon Organization for its support to the IRGC-QF,” he continued in a statement. “New Horizon hosts international conferences that have provided Iranian intelligence officers a platform to recruit and collect damaging information from attendees, while propagating anti-Semitism and Holocaust denial. We are also sanctioning an Iran-based company that has attempted to install malware to compromise the computers of US personnel.”

Additional reporting by AP