US military bases in highest security alert ahead of imminent attacks

All American military bases are now on heightened alert, according to a US official speaking to ABC News.

Bases are now under threat condition "Bravo," which US Department of Defense policy defines as "an increased or more predictable threat of terrorist activity exists."

This is the highest level of security before an attack is considered imminent or likely.

Iran is responding to the U.S.-Israeli operation with missile and drone attacks targeting Israel, regional US bases.