FORT LAUDERDALE, Fla. (AP) — The FBI stated on Wednesday that a suspicious package found outside MacDill Air Force Base in Tampa contained possible energetic materials. An analysis of the contents is still ongoing.

The FBI Tampa reported in a social media statement that the investigation continues without specifics about the materials found. Energetic materials can include explosives, fuels, or propellants, but the agency has not clarified the type involved in this case.

Earlier that day, MacDill Air Force Base implemented a shelter-in-place order following a reported threat. Officials stated, We take all threats seriously and are prioritizing the safety and security of our installation. As policy, we will not disclose specifics about security measures taken. The shelter-in-place was lifted about two hours later, but heightened alert status remains in effect.

Since Tuesday, the base has been under Force Protection Charlie, the military's second-highest security level, allowing for proactive security measures. The advisory urged all personnel to remain vigilant and report any suspicious activities.

MacDill Air Force Base is home to the U.S. Central Command (CENTCOM), responsible for military operations in the Middle East. The base, along with many others, has been on heightened alert due to ongoing tensions related to the situation in Iran.

Last week, all six crew members of a KC-135 refueling aircraft tragically died in a crash during operations related to Iran, with three of the crew linked to MacDill's 6th Air Refueling Wing.