Pope Francis gives the thumbs up at faithful at the end of an open mass celebrated at Calixto Garcia Square in Holguin, eastern Cuba, on Sept. 21, 2015. (credit: LUIS ACOSTA/AFP/Getty Images) Pope Francis gives the thumbs up at faithful at the end of an open mass celebrated at Calixto Garcia Square in Holguin, eastern Cuba, on Sept. 21, 2015. (credit: LUIS ACOSTA/AFP/Getty Images)

WASHINGTON (CBS News/WNEW/AP) — Pennsylvania State Police sent out an alert last week to its department and law enforcement partners as a reminder to be vigilant of persons who may try to impersonate police, fire and first responders in order to carry out an attack in the U.S., reports CBS News’ Pat Milton.

Pennsylvania State Police confirm that a memo was sent out, but was not related specifically to Pope Francis’ visit. Pope Francis is wrapping up his trip in Cuba and arrives in the U.S. on Tuesday.

The official said there are no credible known threats against the Holy Father. However, the official said the alert would apply to the pope’s visit as well.

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House Homeland Security Committee Chairman Michael McCaul said last week that the U.S. has stopped at least one threat made against Pope Francis. The pope’s trip kicks off in Washington with stops at the White House and Capitol Hill, where Francis will be the first pope to address Congress.

Then in New York, he’ll appear before the U.N. General Assembly and visit Saint Patrick’s Cathedral. He concludes his trip in Philadelphia at the 2015 World Meeting of Families, a global Roman Catholic event that happens every three years and is drawing Pope Francis to the United States for his inaugural visit.

McCaul said he received a classified briefing from the Secret Service on the papal visit and that he is “concerned” at the threat of lone wolf attacks.

When Pope Francis hits American streets on Tuesday, a major challenge for police and the Secret Service is figuring out the difference between a threat and what’s “normal” for a VIP who values contact with people above his own safety.

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As one Swiss Guard officer said off the record, when it comes to guarding Pope Francis, “We’ve had to put on our Nikes.”

Security preparations for the pope’s visit include screening checkpoints, airspace restrictions and a ban on selfie sticks and backpacks at papal events. There will be airport-style screenings at checkpoints along his motorcade routes and extensive street closures in every city he is visiting.

COMPLETE GUIDE: Pope Visit 2015

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