US officials said Monica Witt, 39, who worked a decade in Air Force counterintelligence, had an "ideological" turn against her country and defected in 2013, turning over information on US espionage operations against Tehran.

"It is a sad day for America when one of its citizens betrays our country," said Assistant Attorney General John Demers, announcing the indictment.

"This case underscores the dangers to our intelligence professionals and the lengths our adversaries will go to identify them, expose them, target them, and, in a few rare cases, ultimately turn them against the nation they swore to protect," he said.

The US also indicted four Iranians working for the Revolutionary Guard who, using information Witt provided them, targeted her former colleagues in US intelligence with malware and phishing scams in hopes of accessing their computer networks.

The Justice Department has issued arrest warrants for Witt and the four Iranians, who all remain at large. She is believed to be in Iran, officials said.

In a parallel action, the US Treasury announced sanctions on the New Horizon Organization, a Revolutionary Guard group that had invited Witt to Tehran in 2012, and a separate company tied to the hacking effort.

The indictments were dated February 8, but were unveiled Wednesday, on the opening day of a US-led conference in Warsaw, Poland aimed at boosting international pressure on Tehran.

- Farsi language specialist -

Witt's case appeared intertwined with that of Iranian-American television journalist Marzieh Hashemi, who was detained by US authorities in January during a visit to the United States and forced to testify before a grand jury in Washington, DC, where the Witt case was investigated.

The indictment said Witt was recruited during trips to Tehran in 2012 and 2013 with help from an unidentified "Individual A," a dual US-Iranian citizen whose description resembles Hashemi.

Witt served in the US Air Force from 1997 to 2008, becoming an agent in the Air Force Office of Special Investigations, its counterintelligence unit.

A Farsi language specialist, she was deployed to the Gulf area several times on signals intelligence missions, according to the indictment, and had top security clearance giving her access to the identities of clandestine US agents and informants in the field.

After leaving the Air Force, she worked as a defense contractor, but by 2012 her politics had turned.

That year she travelled to Iran to attend an anti-America conference sponsored by the New Horizon Organization.

Later that year she worked with Individual A to make a video critical of the United States, and the two continued to communicate.

She wrote Individual A that she wanted to put her Air Force training "to good use instead of evil."

In February 2013 she again travelled to Tehran for another New Horizon conference, where she met with members of the Revolutionary Guard and told them she wanted to emigrate, the indictment said.

- Wanted to 'do like Snowden' -

But Iranians apparently remained suspicious of her, and she travelled to Afghanistan and Tajikistan, spending months trying to persuade Individual A that she was a genuine turncoat, while threatening to go to Russia and divulge her secrets to WikiLeaks.

In one message she wrote that she might "do like (Edward) Snowden," the former US intelligence contractor who in early June 2013 leaked thousands of documents on the operations of the National Security Agency.

Aided by Individual A, Witt eventually met Iran's ambassador in Tajikistan, who gave her money to fly to Dubai.

On August 28, 2013, she finally defected to Tehran, where she took the name Fatemah Zahra and, according to the indictment, began disclosing classified information to Iranian officials, including the identity of a covert US operative.

There was no detailed explanation of Witt's motives, although there was some suggestion in unconfirmed online records that she had begun to oppose the US wars in Iraq-Syria and Afghanistan.

"Witt's primary motivation appears to have been ideological. She decided to turn against the United States and turn her loyalties to Iran," FBI Executive Assistant Director Jay Tabb told reporters.