A pro-ISIS group recently issued a poster threatening to spill “Christmas blood” in an attack on the Vatican and Pope Francis, the Middle East Research Institute (MEMRI) said Tuesday night.

The Wafa Media Foundation circulated a poster depicting a masked person driving a BMW toward a crowded St. Peter’s Basilica. In the car with the apparent terrorist were a gun, an explosive device, and a backpack. Printed on the poster are the words, “Christmas blood” and, “So wait …” The Pope is scheduled to celebrate Christmas Eve Mass at St. Peter’s on December 24.

[lz_ndn video=33263772]

MEMRI, which monitors terror groups, said that the poster first appeared Tuesday night on Telegram, an anonymous messaging app. The Daily Mail noted that “such posters do not typically warn of a direct threat, but act as a call to action for lone wolf attackers who may be waiting to strike.”

Related: NYC Truck Attack Fulfills Homeland Security Chief’s Prophesy

The day after the poster circulated, Pope Francis signed a donated white and yellow Lamborghini outside the Vatican to be auctioned off in support of raising money for ISIS militants’ victims and also victims of human trafficking and forced prostitution.

The Christmas season at the Vatican attracts thousands of visitors each year, and large seasonal crowds can attract the attention of terrorist groups and lone wolves.

Back on Dec. 19, 2016, Tunisian terrorist Anis Amri slammed a truck into crowds gathered at a Christmas market in Berlin, killing 12 people and wounding 56 others. Using vehicles to strike pedestrians has become a frequent method of attack for terrorists in Europe, making it difficult for police to prepare.

Related: Merkel Feigns ‘Shock’ at Berlin Attack Despite Abundant Warnings

“This kind of attack is very difficult, and probably the most difficult, for law enforcement to protect and prevent,” Steve Gomez, a former FBI agent, told ABC News earlier in November. “So we know the threat exists. Any kind of venue, where there are crowds, we have to recognize that the vehicular attack is the preferred method based on ISIS’ instructions to its followers worldwide, because it’s hard to detect.”

Who do you think would win the Presidency?

“The public must know that a threat exists … They have to recognize that they are in a potentially targeted area and must be alert,” Gomez added. “The crowds are the target … The attacker is looking to kill as many people as possible.”

(photo credit, homepage image: Pope Francis…, CC BY-SA 2.0, by Casa Rosada; photo credit, article image: Pope Francis at Varginha…, CC BY 3.0 BR, by Tânia Rêgo/ABr)