Ten teenagers were taken into custody Saturday in Belgium for plotting terror attacks on Christmas carnivals in the country, according to reports. The arrests came at a time when the risk of such attacks remains high in Europe and several countries have stepped up their security.

Saturday’s arrests were confirmed by Eric Van Der Sijpt, spokesman for the Belgium prosecutor's office, who said the teens received instructions online about how to kill a person and to make a bomb.

“[The teenagers] were recruited by terrorist groups to prepare or commit terrorist acts,” the spokesman said, according to Sputnik news that cited Belgian newspaper Laatste Nieuws.

The identities of those arrested remained unknown.

On Friday, according to a report in German newspaper Der Spiegel — also cited by Sputnik — a 12-year-old boy of Iraqi origin planned to detonate a bomb at a Christmas fair. However, the bomb failed to detonate.

Europe has been on alert since a series of blasts this year in several countries, including Belgium, France, Germany and Turkey. Last month, the U.S. State Department issued an advisory for Americans traveling to Europe, warning them of potential terrorist attacks, primarily during the holiday season.

“Credible information indicates the Islamic State of Iraq and the Levant (ISIL or Daesh) [other names for the Islamic State group], al Qaeda, and their affiliates continue to plan terrorist attacks in Europe, with a focus on the upcoming holiday season and associated events. U.S. citizens should also be alert to the possibility that extremist sympathizers or self-radicalized extremists may conduct attacks during this period with little or no warning. Terrorists may employ a wide variety of tactics, using both conventional and non-conventional weapons and targeting both official and private interests,” the advisory read

The advisory will remain in effect until Feb. 20, 2017.