Paul was one of the speakers Friday at the Iowa Republican Party's Lincoln Day Dinner in Cedar Rapids, NBC News reported. He described Clinton's handling of the deadly February attack on the U.S. consulate in Benghazi, Libya, as "dereliction of duty" and said it "should preclude her from holding higher office."
Clinton is believed to be contemplating a run for president in 2016. Paul, who was elected to the Senate in 2010, is the son of Rep. Ron Paul, R-Texas, a libertarian who has run twice for the Republican nomination.
Paul's attack on Clinton was his biggest applause line from a generally friendly crowd.
The senator also spoke Saturday morning at a Republican breakfast in North Liberty, the Des Moines Register reported.
Paul has said he will not decide until next year whether to enter the 2016 race.