The FBI is investigating possible Iranian hacking attempts targeting the campaigns of President Joe Biden, Vice President Kamala Harris and Republican nominee Donald Trump, CNN and The Washington Post reported.

The investigation is said to have begun in June, when Biden had not yet withdrawn from the election. Three Democratic campaign staffers are said to have received phishing emails, possibly from Iran. The hacking attempt is said to have failed.

In Trump’s case, the hackers could have succeeded in gaining access to the personal email account of Roger Stone, a prominent Republican and Trump confidant. Sources told CNN that the hackers tried to access campaign networks through his account.

Stone was sentenced to three years and four months in prison in 2019. He was convicted of lying to Congress, obstruction of justice and witness tampering. Trump pardoned Stone in the final year of his presidency, sparing him from prison.

A Republican lawyer confirmed to CNN that Stone has been in contact with the FBI and Microsoft about the case, but declined to comment further.

Iran denies the allegations. The US government has not publicly or officially accused Iran of the hack. However, a CNN source says the techniques used by the hackers are similar to those used by Iranian hackers.

Last weekend, Politico published an article about the email hack. The site said it had received emails from an anonymous account containing documents from the Trump campaign. The Trump campaign immediately pointed to Iran. It would be “public information only.”