WASHINGTON — (CNN) Pope Francis and his audiences will see a level of security normally reserved for national political conventions and the presidential State of the Union address during the Pontiff’s U.S. visit next week, authorities said Friday.

That intensity will be especially evident in Philadelphia because Francis will hold his biggest public event there, officials said.

“We believe we have struck that right balance for the public, and we look forward to a safe and successful visit by the Holy Father here,” U.S. Secretary of Homeland Security Jeh Johnson told reporters in a Philadelphia multiagency communications center.

With days to go before Pope Francis’ visit, law enforcement agencies have been dealing with the daunting task of securing travel routes and event sites, which, according to a threat assessment by the FBI and Department of Homeland Security, are attractive targets for terror groups like ISIS and al Qaeda.

But as of Friday, Johnson stated that “we know of no specific, credible threat directed at the Pope’s visit to this city.”

Gatherings planned for the Pope’s visits to Philadelphia, Washington, and New York have been designated “National Special Security Events,” which require a massive amount of coordination and planning by multiple law enforcement agencies.

The preparations come amid a new ABC News report of a 15-year-old boy who was arrested and accused of plotting an ISIS-inspired attack on the Pope when he visits Philadelphia.

Michael Balboni, former deputy secretary for public safety and homeland security adviser for New York state, said authorities are worried about people who may want to get close to a Pope who likes contact with the crowd.

Balboni also noted how the Islamic extremist group ISIS recently stated it wants to raise the ISIS flag over the Vatican.

The Pope’s visit to the United States would make for an attractive target for ISIS.

“This is still their major target, so there is an opp to strike a blow against Christianity and strike a blow against their hated enemy, the United States,” Balboni said.

A September bulletin distributed to law enforcement around the country and obtained by CNN highlights some of the recent terror-related arrests of alleged homegrown violent extremists in the United States and expresses concerns about potential lone wolf attackers “because of the difficulty in discovering such individuals or independent groups until they are operational.”

The Pope’s visit is also deemed to be “a powerful motivator for groups or individuals with anti-Catholic or anti-Christian viewpoints” who may justify violence for religious reasons, citing recent attacks carried out by al Qaeda or ISIS-inspired groups such as Boko Haram in Nigeria or al-Shabaab in Kenya.

Federal law enforcement estimates some events, such as an open-air Sunday Mass in Philadelphia, will attract crowds of well over a million people, making it a challenging environment to secure.

But in an effort to identify potential threats, a number of behavioral indicators were listed that could be deemed “preoperational surveillance” or “attack planning,” including “suspicious purchases of dual-use items that could be used to construct an explosive device, unusual or prolonged interest in motorcade movement dynamics and security, and discreet use of cameras or video recorders, sketching, or note-taking.”

Though the intelligence provided in the bulletin is “absent a specific, actionable threat,” the information was circulated in a collaborative attempt to “aid law enforcement and first responders in identifying and mitigating threats.”

The papal visit also presents unique challenges because Pope Francis doesn’t want security so heavy it prevents his interaction with pilgrims, and because of perceived threats from potential attackers not on the radar of law enforcement.

In planning safety measures, federal and local authorities met with Philadelphia businesses and community groups to ensure the overall plan “keeps the city of Philadelphia going,” Johnson said.

“I’m struck by the areas that will not be closed out and that will continue to be open access for large segments of the public,” Johnson added, referring to distant security perimeters around the Pope’s visit.

Francis will arrive on U.S. soil in Washington on Wednesday and then travel to New York on Thursday.

The Pope will arrive in Philadelphia the next Saturday, September 26.

The Pontiff’s initial reason to visit the United States was to attend Philadelphia’s World Meeting of Families Congress, an international event of prayer, catechesis and celebration of marriage and family, said Philadelphia Mayor Michael A. Nutter.

“I’m very proud. I’m very excited,” Nutter told reporters.

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