Several US military bases across Europe were put on a heightened state of alert, France-Press reported. The alert level at those bases was raised to Force Protection Condition “Charlie”, the second highest alert level, ABC News and CNN reported, citing officials who spoke on condition of anonymity.

That status “applies when an incident occurs or intelligence is received indicating some form of terrorist action or targeting against personnel or facilities is likely,” the US army says on its website.

The highest level, Delta, applies when a terrorist attack is ongoing or “imminent.”

“Due to a variety of factors that could impact the safety of US military personnel and their families deployed in the European theater, US European Command is redoubling its efforts to emphasize the need for vigilance during the summer months,” the Pentagon said.

The US State Department is currently advising US citizens in Germany, where US Forces Europe is headquartered, to exercise extreme caution due to the risk of terrorist attacks.