The United States on Wednesday indicted a former counterintelligence agent with the U.S. Air Force for aiding Iran in what Washington characterized as a cyber-spying operation targeting U.S. intelligence officers.

Monica Elfriede Witt, who defected to Iran in 2013 and is currently at-large, is accused of revealing classified information to Iran.

Assistant Attorney General John Demers, the head of the Justice Department's national security division, says, "It is a sad day for America when one of its citizens betrays our country."

As part of its action, the United States also charged four Iranian nationals who it said were involved in the cyber attacks.

Washington also sanctioned two Iran-based firms - New Horizon Organization and Net Peygard Samavat Company - and several individuals associated with the two groups.

U.S. officials said Witt supplied classified information about U.S. intelligence officers after defecting to Iran in 2013.

Witt was recruited for the operation after attending two international conferences organized by New Horizon, which supported efforts by Iran's Revolutionary Guard's Quds Force to recruit and collect intelligence from foreign attendees, they said.

They said Witt served as a counterintelligence officer in the Air Force from 1997 until 2008, and worked as contractor for two years after that.

Net Peygard targeted current and former U.S. government and military personnel with a malicious cyber campaign, officials said.