Hackers were able to break into the email accounts of Roger Stone, a longtime GOP operative and adviser to former President Donald Trump, in hopes of compromising the accounts of his senior campaign officials, according to new media reports.

The FBI said Monday it is investigating a “cyberintrusion” aimed at the Trump campaign, just days after the former president said Iran was targeting his reelection bid. Trump’s remarks came after multiple media outlets, including Politico, received anonymous emails with internal Trump campaign documents attached, including a dossier on his running mate, Ohio Sen. JD Vance.

The Washington Post reports the FBI is now investigating a broad range of cyber attacks, including phishing attempts received earlier this year by staffers working on the then-Biden-Harris campaign. The publication said another phishing attempt appeared to have compromised Stone’s email, which was then used to send emails to people in the Trump campaign.

The nefarious messages were designed to encourage recipients to click on a link. If they did so, the Post reports, the hackers may have been able to intercept other emails.

The U.S. has not formally accused Iran of being responsible for the hack.

“I was informed by the authorities that a couple of my personal email accounts have been compromised,” Stone told The Washington Post on Monday. “I really don’t know more about it. And I’m cooperating. It’s all very strange.”

Microsoft confirmed Friday that a group run by Iran’s Islamic Revolutionary Guard Corps had compromised the account of a former senior adviser to a presidential campaign, part of a growing campaign of “foreign malign influence.” It did not name the adviser or campaign that was targeted.

Iran has rejected accusations it is involved. The country’s mission to the United Nations told The New York Times the Iranian government “neither possesses nor harbors any intent or motive to interfere in the United States presidential election.”

It’s unclear how broad the phishing attempts were. The Harris campaign told the media outlets it remained “vigilant” in its effort to defend against cyberthreats and that it was not aware of any security breaches.

An adviser for the Trump campaign told the Post it had taken new measures to secure its email servers and staffers have been informed to keep sensitive documents or information out of such messages.