U.S. authorities foiled attacks planned around the Fourth of July, arresting more than 10 people in the month before the holiday who were inspired by Islamic State online recruitment, FBI Director James Comey said on Thursday.
"I do believe our work disrupted efforts to kill people likely in connection with July 4th," Comey told reporters at the headquarters of the Federal Bureau of Investigation. He did not detail the number of plots uncovered or their targets.
Separately, a national security source said multiple overseas plots by Islamic State sympathizers had also been halted in recent days.
The FBI and the U.S. Department of Homeland Security had warned local law enforcement to be on alert for attacks around the July 4 holiday celebrating the 1776 U.S. Declaration of Independence. No such attacks occurred.
Authorities' concern heightened around the holiday as Islamic State leaders called for followers to do what they could wherever they could to carry out violence on behalf of the militant group.
Comey described the tactic as "crowd sourcing terrorism" and said the FBI had accepted the heightened state as the "new normal."
Some of those arrested were communicating with Islamic State via encrypted data, a second U.S. security source said.
The FBI has pressured tech companies to remove encryption that gives users privacy protections that cannot be broken by law enforcement.
Comey estimated that dozens of people influenced by Islamic State have "gone dark" and disappeared from the FBI's watch because of encrypted data.
The United States is engaged in a military campaign with allies in the Middle East to fight Islamic State militants who have taken over parts of Iraq and Syria and created cells in other countries racked by conflict in the region.