The Islamic State group, also known as ISIS, published a photo of Pope Francis in the latest issue of its magazine, labeling him “the crusader pope” and provoking fears about the pontiff’s safety ahead of his historic visit to the U.S., NBC News reported. Security officials said, however, they had not received any credible threats against the pope ahead of his U.S. visit, which began in Washington Tuesday afternoon.

The ISIS magazine, Dabiq, is an English-language publication aimed at recruiting foreigners to join the terrorist group. In an issue released last week, a photo showed Istanbul’s highest Muslim religious official with the pope and called the official an “apostate.” An intelligence official who spoke with NBC News said the caption was vague but could lead to dangerous interpretations.

The pope has spoken out against ISIS, calling the group an “unjust aggressor” last year. "In these cases, where there is an unjust aggression, I can only say that it is licit to stop the unjust aggressor," he said, according to the Associated Press.

In 2014, Dabiq ran a cover image of the Vatican with ISIS’ notorious black flag flying above St. Peter’s Square. An article in that issue specifically called for attacks against the Catholic Church.

The pope’s visit comes amid heightened security measures in Washington, New York and Philadelphia. Thousands of law enforcement officials have prepared for the pontiff’s visit to the U.S., with some Secret Service members even traveling to Rome to see how the Catholic Church’s leader interacts with large crowds, the New York Times reported. The Secret Service was scheduled to take the lead in protecting the pope.

Security officials have prepared for various scenarios, including the possibility that a terrorist would dress as a police officer or first responder, International Business Times reported. A memo released yesterday was titled “First Responder Impersonators: The New Terrorist Threat.”

Thousands of people are expected to see the pontiff when he appears in public places this week, including in front of the capital in Washington and Central Park in New York.