U.S. authorities thwarted plots to kill people in the United States around the July 4 holiday, FBI Director James Comey said on Thursday.

Comey told reporters more than 10 people inspired by the Islamic State's recruitment online have been arrested over the past four weeks, some of which were focused on attacks around the July 4 holiday.

FBI and the Department of Homeland Security issued a warning to local law enforcement to be on alert for attacks around July 4. No such attacks occurred.

Comey did not give the details on the number of plots thwarted or their targets.

He said dozens of people in the United States who are suspected to be under the influence of Islamic State militants have "gone dark" because of encrypted data.