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.

Federal agencies have warned of a possible lone-wolf terror threat to July 4 celebrations, with the FBI calling such attackers the biggest risk to events like the Macy’s fireworks show in New York.

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