U.S. military bases across Europe are stepping up security precautions following the deadly terrorist attacks in Paris and anti-terror raids sweeping the continent. While there is no imminent threat, the increased security presence and patrols in and around military facilities are seen as "prudent" measures to avert or discourage any attacks, said the U.S. European Command (EUCOM) in Brussels.

One senior U.S. military official told NBC News that there are an estimated 4,000 to 5,000 extremists "trained in Iraq or Syria, who have returned to Europe” and pose a potential threat to American service members and their families.

The increased security protocols were implemented Tuesday, although EUCOM officials declined in a statement to specify the measures. While they might vary from base to base, they typically involve the inspecting of cars, bag checks and patrols, the Stars and Stripes newspaper reported. EUCOM and U.S. military throughout Europe have been on a high alert level, although these enhanced security measures weren't immediately instated after the deadly attacks in Paris two weeks ago that left 17 dead.

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