Attacks perpetrated by lone actors are the biggest terrorism threat to July 4th festivities in New York City and elsewhere, federal authorities said in a threat assessment obtained by CNN.

The Department of Homeland Security and the FBI are concerned about the potential for copycat attacks from the New Orleans terror attack, as well as homegrown extremists.

Intelligence bulletins sent out ahead of the holiday warn of copycat attacks and homegrown extremists targeting July 4 celebrations in City and San Francisco.