Hackers based in Russia were behind two recent attempts to breach state voter registration databases, U.S. intelligence officials tell NBC News.
One official said the attacks have been attributed to Russian intelligence agencies.
"This is the closest we've come to tying a recent hack to the Russian government," the official said.
That person added that "there is serious concern" that the Kremlin may be seeking to sow uncertainty in the U.S. presidential election process.
The incidents led the FBI to send a "flash alert" earlier this month to election officials nationwide, asking them to be on the lookout for any similar cyber intrusions.
The bulletin does not identify the targeted states, but officials told NBC News they were Illinois and Arizona.