US officials said Monica Witt, who worked for years in US Air Force counterintelligence, had an "ideological" turn against her country and defected in 2013, turning over information on US intelligence 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 other hacking tools 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.

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

After leaving the Air Force, she worked as a defense and intelligence contractor, but by 2012 her politics had begun to turn.

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

She returned to Iran the next year and began disclosing classified information to Iranian officials, including on her former colleagues in the US intelligence community.

She revealed to the Iranians a "highly classified intelligence collection program" as well as the true identity of a US intelligence officer, Demers said.

According to an undated FBI missing persons declaration regarding Witt, she had not been in contact with anyone since 2013.

The announcement, which also included sanctions on the New Horizon Organization, organization officials, and a company tied to the hacking effort, came on the opening day of a US-led international conference in Warsaw, Poland aimed at boosting pressure on Tehran.