American intelligence officials say hackers based in Russia are to blame for two recent attempts to breach voter registration databases in a US state.
In the two attempts, data from as many as 200,000 voter records in the US state of Illinois was stolen, the officials told NBC News.
They said that the incidents fueled concerns that the Russian government might be seeking to interfere in the US presidential election.
One of the officials claimed that "there is serious concern" that Moscow was trying to create uncertainty in the US presidential election process.
The official, who spoke on condition of anonymity, said that the attacks were attributed to Russian intelligence services.
"This is the closest we've come to tying a recent hack to the Russian government," the official said.
The attacks caused the FBI to issue a "flash alert" to election officials nationwide earlier this month. The agency urged them to remain vigilant in the face of any similar cyber intrusions.
"The FBI is requesting that states contact their Board of Elections and determine if any similar activity to their logs, both inbound and outbound, has been detected," the alert said.
Meanwhile, two other officials said that US intelligence agencies are not certain yet that the Russian government may be wanting to hack into voter records.
However, they said it was not clear whether the hackers were planning a covert intelligence operation aimed at destabilizing the US political process.
The incident was first reported by Yahoo News and the alert provided IP addresses linked to the hack attempts, but it did not mention Russia.
According to the FBI alert, one of the IP addresses was associated with both breaches.
US officials have previously expressed concerns about Russia's involvement in the hacking of the Democratic Party organizations.
Under a worst-case scenario, Russia's sophisticated hackers could attack financial systems, power grids and other critical infrastructure, the intelligence officials said earlier this month.
Russia has denied responsibility for hacking the emails of the Democratic National Committee (DNC) and a computer network used by Democratic presidential nominee Hillary Clinton's campaign ahead of the November vote.