Ahead of this July 4th holiday, law enforcement in major U.S. cities is on guard for a new round of terror threats.

Local and state law enforcement will be on the look-out for potential threats.

While there are no specific plots that've been uncovered, intelligence sources tell ABC News it's likely you'll see a stronger security presence this year.

Authorities are worried about the Al Qaeda affiliate in Yemen, which recently planned a new underwear bomb threat.

And they are concerned about "lone wolves" belonging to no particular group - who want to create havoc during an important American holiday.