A prominent U.S. Senator has asked the FBI to investigate claims of possible Russian interference in the country's upcoming presidential election, The New York Times reported Monday.

Writing in a letter to FBI Chief James B. Comey Jr., Senate Minority Leader Harry Reid claimed that Russian interference is “more extensive than is widely known and may include the intent to falsify election results.”

Speaking in a recent interview, Reid said he feared that Russia wanted to “tamper with this election” based on briefings from senior intelligence officials.

The FBI has allegedly warned two U.S. states of foreign hackers which had hacked into their computer systems, in one case exporting voter registration data, The New York Times reported.

The states in question have not been confirmed, but have been named in the media as Arizona and Illinois.

Matt Roberts, a spokesman for Arizona’s secretary of state, later announced that the FBI had told state officials that the Kremlin was behind the cyber attack.

Cyber security experts have previously accused Russian intelligence agencies of hacking networks of the Democratic National Committee last month.

Washington has not formally accused Moscow of orchestrating the breaches, despite U.S. intelligence informing the White House they were “highly confident” of Russian involvement, The New York Times reported.

The Kremlin denies all allegations, calling the claims “absurd.”

The U.S. presidential elections are due to take place on Nov. 6, 2016.