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. The Department of Homeland Security and the FBI are concerned about the potential for copycat attacks from the New Orleans terror attack on New Year's Day,

The FBI and Department of Homeland Security have said lone wolf attacks pose the biggest threats to July 4 celebrations this year in City and San Francisco. Intelligence bulletins sent out ahead of the holiday warn of copycat attacks and homegrown extremists,