The FBI is investigating suspected attempts to hack mobile phones used by Democratic Party officials as recently as the past month, people with direct knowledge of the attack and the investigation told Reuters on Tuesday.
The revelation underscores the widening scope of the U.S. criminal inquiry into cyber attacks on Democratic Party organizations, including the presidential campaign of its candidate, former U.S. secretary of state Hillary Clinton.
U.S. officials have said they believe those attacks were orchestrated by hackers backed by the Russian government, possibly to disrupt the November 8 election in which Clinton faces Republican Party candidate Donald Trump. Russia has dismissed the allegations.
The more recent attempted phone hacking also appears to have been conducted by Russian-backed hackers, two people with knowledge of the situation told Reuters.
FBI representatives had no immediate comment, and a Clinton campaign spokesman said they were unaware of the suspected phone hacking.
The Democratic National Committee (DNC) did not respond to a request for comment, and the Democratic Congressional Campaign Committee (DCCC) had no immediate response.
The FBI is already investigating a previous hacking of DNC computers, which was followed by 20,000 emails being published and showing a DNC favorable to Clinton over Bernie Sanders.
The leak led DNC chairwoman Debbie Wasserman Schultz to announce her resignation before she bowed out of the convention altogether.
According to Tuesday’s report, FBI agents had approached a small number of Democratic Party officials to discuss concerns their mobile phones may have been compromised by hackers.
It was not clear how many people were targeted by the hack or whether they included members of Congress, a possibility that could raise additional security concerns for U.S. officials.
If they were successful, hackers could have been able to acquire a wide range of data from targeted cell phones, including call data, text messages, emails, photos and contact lists, one person with knowledge of the situation told Reuters.
U.S. investigators are looking into whether hackers used data stolen from servers run by Democratic organizations or the private emails of their employees to get access to cell phones, one person said.
Clinton said during Monday's presidential debate there was "no doubt" Russia has sponsored hacks against "all kinds of organizations in our country" and mentioned Russian President Vladimir Putin by name.
"Putin is playing a really tough, long game here. And one of the things he's done is to let loose cyber attackers to hack into government files, to hack into personal files, hack into the Democratic National Committee," Clinton said.
Trump countered by noting that there was no definitive proof that Russia had sponsored the hacks of Democratic organizations.
"I don't think anybody knows it was Russia that broke into the DNC," he said. "It could be Russia, but it could also be China. It could also be lots of other people."