Authorities on high alert for possible terror attacks on 4th of July

LOS ANGELES (KABC) -- A bulletin warning of a possible terror attack was sent out to 18,000 police agencies across the country for the Fourth of July holiday.

Unlike past alerts during the holidays, the concern is focused on a possible lone wolf attack inspired by the terrorist group ISIS.

Thursday's massive response to a false alarm at the Navy shipyard in Washington D.C. is some indication of the heightened state of concern. Some experts say the warnings being issued need to be taken seriously.

In Europe, U.S. military bases are canceling Fourth of July celebrations because of the terror concerns. U.S. authorities have also made a number of arrests of suspects they say are linked to the ISIS terror network.

A larger police presence will be in public places where crowds may gather during the holiday weekend.