The Department of State warned Islamic State terrorists could target European Christmas markets three weeks before Monday’s attack in Berlin.

Germany authorities confirmed that 10 people were killed and more than 50 were injured when an attacker slammed a truck into a group of pedestrians attending the Berlin Christmas market. It is currently unclear whether or not ISIS is responsible for the attack, although police are considering it intentional.

“U.S. citizens should exercise caution at holiday festivals, events, and outdoor markets,” the State Department warned in a travel alert Nov. 21. “Credible information indicates the Islamic State of Iraq and the Levant (ISIL or Daesh), al-Qaida, and their affiliates continue to plan terrorist attacks in Europe, with a focus on the upcoming holiday season and associated events.”

A Europol report from Dec. 2 warned that terrorist organizations may engage in “several dozen” attacks over the holiday season as ISIS fighters continue to return to their home countries.

The Berlin attack mirrors a previous attack in Nice, France, in July, which killed 86 people and injured 434. ISIS propaganda outlets published instruction booklets detailing how followers could engage in similar attacks shortly thereafter.

ISIS called for attacks on Christians after taking credit for the bombing of a Coptic Christian Church last week.

“Let all the disbelievers and apostates in Egypt and everywhere know that our war on polytheism is ongoing, and that the State of the Caliphate – with permission from Allah the Almighty – will continue to spill their blood and grill their bodies, so that there is no sedition and the religion is all for Allah,” said ISIS in a statement, according to SITE Intelligence Group.

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