Federal investigators looking into disclosures of classified information about a cyber-operation that targeted Iran's nuclear program have increased pressure on current and former senior government officials who are suspected of involvement, according to people familiar with the investigation. Prosecutors are pursuing "everybody — at pretty high levels, too," said one person.

The inquiry, which was started by Attorney General Eric Holder last June, is examining leaks about a computer virus developed jointly by the United States and Israel that damaged nuclear centrifuges at Iran's primary uranium enrichment plant. The U.S. code name for the operation was Olympic Games, but the wider world knew the mysterious computer worm as Stuxnet.

The FBI and prosecutors have interviewed several current and former senior government officials in connection with the disclosures, sometimes confronting them with evidence of contact with journalists, according to people familiar with the probe.

The Obama administration has prosecuted six officials for disclosing classified information, more than all previous administrations combined. But the Stuxnet investigation is arguably the highest-profile probe conducted yet.

Knowledge of the virus was likely to have been highly compartmentalized and limited to a small number of Americans and Israelis.