The Senate minority leader, Harry Reid of Nevada, asked the F.B.I. on Monday to investigate evidence suggesting that Russia may try to manipulate voting results in November.

In a letter to the F.B.I. director, James B. Comey Jr., Mr. Reid wrote that the threat of Russian interference “is more extensive than is widely known and may include the intent to falsify official election results.” Recent classified briefings from senior intelligence officials, Mr. Reid said in an interview, have left him fearful that President Vladimir V. Putin’s “goal is tampering with this election.”

News reports on Monday said the F.B.I. warned state election officials several weeks ago that foreign hackers had exported voter registration data from computer systems in at least one state, and had pierced the systems of a second one.

The bureau did not name the states, but Yahoo News, which first reported the confidential F.B.I. warning, said they were Arizona and Illinois. Matt Roberts, a spokesman for Arizona’s secretary of state, said the F.B.I. had told state officials that Russians were behind the Arizona attack.