"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.

A lone wolf actor poses the biggest threat to Fourth of July celebrations in New York and San Francisco, according to multiple intelligence bulletins obtained by ABC News.