NYPD chief: Pope will "have 6,000 additional guardian angels"

The New York Police Department is facing an unprecedented security challenge starting Thursday, as Pope Francis visits New York City at the same time as 170 other world leaders.

New York Police Commissioner Bill Bratton told "CBS This Morning" Tuesday that there are no known threats against Francis but said his force would be prepared to assist the pope's own security detail.

Historic security precautions to surround Pope Francis in U.S.

"He's gonna have 6,000 additional guardian angels around him," Bratton said. "But I'm assuming he's bringing a few of his own so we'll take all the help we can get."

Bratton said that the NYPD was coordinating with officials in Philadelphia and Washington, the two other stops on the pope's U.S. tour, in order to create a "seamless operation between the three cities."

While there are no credible threats against the pope, last week, Pennsylvania police warned of people impersonating officers to carry out an attack. And last month a 15-year-old in New Jersey was arrested, who investigators say may have been communicating with the Islamic State of Iraq and Syria (ISIS) as part of a plan to build a bomb and carry out an attack against a visiting diplomat or the pope.

Pope Francis to begin historic U.S. visit

NYPD Deputy Commissioner for Intelligence and Counterterrorism John Miller said that officials in New York, Philadelphia and Washington have reviewed the "threat picture" from ISIS, al Qaeda and other terror groups. He said they have even reviewed every attempt on every pope's life going back to the late 1970s.

"We wanted to remind everybody on these details in all three cities about the way these things have happened in the past, the different ways they've been put together," Miller said.

Miller said that one of the biggest challenges for intelligence officials is that terror threats are now Internet-driven.

"In terms of the threat picture and that means if the conspiracy is just between a glowing laptop screen in someone's dark bedroom and their mind, that's very difficult to penetrate from an intelligence standpoint," Miller said.

Bratton said that despite the security challenges, the three cities' police forces are "tightly coordinated" with the FBI and Secret Service to provide security for Francis.

"It's a celebratory event for everybody else," Bratton said. "For us, this is a security event, one of the highest level."