The U.S. military has raised the security protection measures it is taking at its bases throughout Europe, asking service members to be more vigilant and keep a lower profile due to a combination of threats it is seeing across the region.

U.S. European Command said in a statement Sunday that a "variety of factors play into the safety of U.S. military community abroad."

Increasing the threat level to Charlie — the second-highest of five levels for service members — is the result of a combination of events occurring across Europe, including elections in France and the U.K., the upcoming Olympics and other major sporting events, and the ongoing wars in Ukraine and Gaza, according to two U.S. officials who spoke on the condition of anonymity to The Associated Press to provide additional details. But they said they were unaware of any specific threat.

"It is just a dangerous time right now," said CBS News national security contributor Samantha Vinograd, who was formerly the assistant secretary for counterterrorism and threat prevention at the Department of Homeland Security. "Large, mass gatherings are oftentimes a period of heightened concern."

She also noted New York Times' reporting that Russian threats against the U.S. for its support for Ukraine are a factor.

Pentagon deputy press secretary Sabrina Singh would not say Monday whether bases in the Middle East, Africa or the Indo-Pacific were at similar increased force protection levels. However, one of the officials said that many of those bases, especially bases throughout the Middle East and Africa, already maintain higher security levels.

Raising the threat level to Charlie means additional security measures will be in place at U.S. military installations, but it's up to each commander's discretion to determine what those measures are. It also means service members and their families who are living in each community should be more aware of their surroundings and maintain a lower profile, one of the officials said.

Vinograd told CBS News on Tuesday that the action has led to "heightened security measures at the bases" and "the curtailment of what are known as nonessential personnel coming to the bases, and other measures to keep its people safe." 

FBI and Homeland Security officials in May issued a worldwide security alert, warning U.S. citizens of potential terrorist attacks abroad. The threat warning was a result of intelligence citing threats by ISIS against Pride events in parts of Europe, three sources told CBS News. 

"Overall, it is a heightened period from a terrorism-related perspective and the military is clearly taking actions to ensure operational safety," said Vinograd.  

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• National Security
• Terrorism
• Olympics
• Russia
• United States Military
• Vladimir Putin