The FBI is investigating suspected attempts to hack mobile phones used by Democratic Party officials as recently as the past month, four people with direct knowledge of the attacks and the investigation told Reuters.

The revelation underscores the widening scope of the criminal inquiry into cyberattacks on Democratic Party organizations, including the presidential campaign of its candidate, former 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 Nov. 8 election, in which Clinton faces Republican candidate Donald Trump.