Final answer:
The FPCON level that would be declared as a localized warning where an attack has occurred is FPCON Delta.
Step-by-step explanation:
In the context of security threat levels, FPCON (Force Protection Condition) is a system used by the United States Department of Defense to indicate the levels of security measures to be taken in response to various threats. If a localized warning has been issued due to an attack in a specific area, the FPCON level that would be declared is FPCON Delta. FPCON Delta is the highest threat level, indicating that a terrorist attack has occurred or is imminent.