The U.S. FBI said on Monday it was investigating after Donald Trump's presidential campaign said its internal communications were hacked and blamed the Iranian government.
The former president said on Saturday that Microsoft had informed his campaign that Iran had hacked one of its websites. He said Iran was "only able to get publicly available information."
The Iranian government has denied that it hacked the Trump campaign.
Trump's campaign has pointed to a report on Friday by Microsoft researchers which indicated that Iranian government-linked hackers tried breaking into the account of a "high-ranking official" on a U.S. presidential campaign in June.
The report added that the hackers took over an account belonging to a former political adviser and then used it to target the official. It did not provide further details on the targets' identities.
