Several U.S. military bases in European countries such as Germany and Italy were placed on an increased security alert over the weekend.

Bases such as the U.S. Army Garrison in Stuttgart, Germany, the U.S. Army’s Rheinland-Pfalz base, and the U.S. Army’s Ramstein Air Base were among the bases that were placed on a threat level of “Charlie,” according to Stars and Stripes.

This came after the U.S. European Command (EUCOM), which is headquartered in Stuttgart, issued an increased threat level to “Charlie.”

Other U.S. military bases such as the U.S. Army Garrison Rheinland-Pfalz’s base in Baumholder, Germany, and other military bases in Romania, Bulgaria, and the Aviano Air Base in Italy also increased their threat level to “Charlie.”

The outlet noted that another base in Germany, the Spangdahlem Air Base, directed military members not to wear their uniforms off base, or even when commuting to work.

According to the U.S. Army’s website, Charlie is one of five security levels in the Force Protection Condition (FPCON).

The lowest threat level is, “Normal,” which is followed by threat level “Alpha,” which applies when “there is an increased general threat of possible terrorist activity against personnel or facilities,” according to the U.S. Army’s website.

Bravo is the third threat level, which “applies when an increased or more predictable threat of terrorist activity exists.”

After the Bravo threat level is Charlie, the second highest threat level, which “applies when an incident occurs or intelligence is received” that indicates “some form of terrorist action or targeting against personnel or facilities is likely.”

The “Delta” threat level, which is the highest, “applies in the immediate area where a terrorist attack has occurred or when intelligence has been received that terrorist action against a specific location or person is imminent,” according to the U.S. Army’s website.

EUCOM explained in a statement that it is “constantly” reviewing “factors” that may affect “the safety of the U.S. military community abroad,” according to the outlet.

A United States official stated that the current threat level had not been seen “in at least 10 years,” according to CNN.