The US has charged a former Air Force officer with spying for Iran in an operation that targeted her fellow officers, according to an indictment unsealed in a federal court.

Monica Witt, who was also a former counterintelligence officer for the Air Force Office of Special Investigations, defected to Iran in 2013, according to the indictment on Wednesday. She remains at large, CNN reported.

The Federal Bureau of Investigation (FBI) says that Witt, 39, was last seen in southwest Asia in July 2013.

According to the Department of Justice, Witt was targeted and recruited by Iran and after she defected, she allegedly revealed to Tehran the existence of a “highly classified intelligence collection programme” and the identity of a US intelligence officer, “thereby risking the life of this individual”.

Witt is accused of sharing the US government secrets, including the name of agents and specifics of operations, with Iran as early as January 2012. In a charging document, investigators said she was deployed by the US to locations in the Middle East to conduct classified counterintelligence operations.

Four Iranian citizens were also charged with attempting to install spy software on computers belonging to Witt’s colleagues.

“It is a sad day for America when one of its citizens betrays our country,” Assistant Attorney General John Demers said.

Prosecutors said that Witt had been granted the highest level of US security clearance and worked in the US Air Force from 1997 to 2008.

The US Department of Treasury also sanctioned two Iranian companies – New Horizon Organization and Net Peygard Samavat Company – for their role in the plot.

Officials say that she sent a message to her Iranian contact in 2012 saying, “I loved the work, and I am endeavouring to put the training I received to good use instead of evil. Thanks for giving me the opportunity.”

Witt, according to investigators, was recruited after attending two conferences hosted by New Horizon Organization, which was working on behalf of the Iranian National Guard’s Quds Force to collect intelligence on attendees.

The FBI had earlier stated in its missing person’s poster that Witt was working as an English teacher in either Afghanistan or Tajikistan, and had lived overseas for more than a year before vanishing.

While in Iran, she allegedly converted to Islam during a TV segment after identifying herself as a US veteran and delivered several broadcasts in which she criticized the US.