The F.B.I. said on Monday that it was investigating whether the Trump campaign had been hacked, days after the former president said Iran had launched a cyberattack.

The bureau did not specifically name Iran or former President Donald J. Trump but referred to news reports about a “campaign cyberintrusion.”

“We can confirm the F.B.I. is investigating the matter,” it said in a statement.

The F.B.I. has repeatedly warned about foreign countries meddling in the U.S. election, including using artificial intelligence to spread misinformation. The F.B.I. has said Iran, China and Russia were at the top of the list. Russia has a long history of trying to sow chaos in American elections, targeting the Democratic National Committee in 2016.

The Trump campaign has so far provided no evidence of Iran’s involvement, but on Friday Microsoft said a hacking group run by the intelligence unit of Iran’s Islamic Revolutionary Guards Corps had breached the account of a “former senior adviser” to a presidential campaign.

It added that the group then used to the account to send fake emails, known as “spear phishing,” to “a high-ranking official of a presidential campaign” in an effort to break into the campaign’s own accounts and databases.