ALEXANDRIA, Va. » Former national security adviser Condoleezza Rice said Thursday that she was stunned when she learned a classified mission to thwart Iran’s nuclear weapons ambitions had been leaked to the news media.

Rice told jurors in an ongoing criminal trial outside Washington that the program was one of the most closely held operations during her tenure as national security adviser in the first term of President George W. Bush’s administration.

The plan called for using a Russian CIA asset nicknamed "Merlin" to funnel deliberately flawed nuclear blueprints to the Iranians.

Prosecutors believe ex-CIA case officer Jeffrey Sterling of O’Fallon, Missouri, illegally disclosed details of the program to New York Times reporter James Risen because he was bitter about his treatment at the agency.

Sterling denies leaking any information to Risen. Defense lawyers say the leak could have come from anywhere and that Sterling has faced unfair suspicion because he sued the CIA for racial discrimination.

In earlier testimony Thursday, an unidentified CIA manager testified under cross-examination that more than 90 people knew about the covert mission.