"The FBI and DHS are concerned about possible copycat ... Others have attempted to conceal and pre-position improvised explosive devices (IEDs) to supplement a vehicle attack, the PSA added.

U.S. officials have put several Mexican border towns near Texas under the highest-level travel advisory amid gun battles, ...

The warning was issued because of "increasingly frequent gun battles" and the discovery of "improvised explosive devices (IEDs)." ...

"The FBI and DHS are concerned about possible copycat or retaliatory ... Others have attempted to conceal and pre-position improvised explosive devices (IEDs) to supplement a vehicle attack, the PSA ...