"We are enhancing security measures and coordinating intelligence-sharing to proactively address potential risks," a DHS spokesperson told Newsweek.

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.

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