Several U.S. military bases across Europe are now operating under a heightened state of alert, ABC News has confirmed.

The alert level of Force Protection Condition (FPCON) “Charlie” was put in place over the weekend, according to two U.S. officials.

According to the U.S. Army, Charlie is the second highest state of alert that “applies when an incident occurs or intelligence is received indicating some form of terrorist action or targeting against personnel or facilities is likely.”

In a statement provided to reporters, U.S. European Command said it’s “constantly assessing a variety of factors” on security and safety.

“For operational security reasons, we will not get into specific measures, but we remain vigilant,” EUCOM wrote, in part.

The development was first reported by Stars and Stripes, an independent military publication.