Security services have intervened to prevent a threat in advance of the Pope's visit to the United States, it has been disclosed. 

Michael McCaul, chairman of the House Committee on Homeland Security, told ABC News that the US Secret Service had already "disrupted" one incident.

McCaul, himself a Catholic, said he was "concerned" about the Pope's visit.

Pope Francis visits Cuba, New York, Washington and Philadelphia at the end of this month.

McCaul said he had been briefed by the Secret Service: "The Pope is a very passionate man. He likes to get out with the people and with that comes a large security risk. We are monitoring very closely threats against the Pope as he comes into the United States. We have disrupted one particular case in particular, but as that date approaches, I think we're all very, being very vigilant to protect him as he comes into the United States."

The Pope will use an open Popemobile similar to that in his recent visit to Ecuador for events in the US such as a motorcade through Central Park. Bullet-proof glass-encased Popemobiles were used for a time after the assassination attempt on Pope John Paul II in 1981.

McCaul's concerns represent a recognition of the heightened security risks due to Pope Francis' aim to be as open as possible and to meet personally as many people as possible. The visit also will have its share of pomp and ceremony, as Associated Press reported.

President Barack Obama will receive him personally with a rare air-side greeting as the Papal plane arrives from Cuba at Washington's Joint Base Andrews on 22 September. The official red carpet will be rolled out when he becoems the third Pope to visit the White House the following day.  

President Obama told this year's National Prayer Breakfast: "Whatever our beliefs, whatever our traditions, we must seek to be instruments of peace, and bringing light where there is darkness, and sowing love where there is hatred. And this is the loving message of His Holiness, Pope Francis.

"And like so many people around the world, I've been touched by his call to relieve suffering, and to show justice and mercy and compassion to the most vulnerable; to walk with The Lord and ask 'Who am I to judge?' He challenges us to press on in what he calls our 'march of living hope'. And like millions of Americans, I am very much looking forward to welcoming Pope Francis to the United States later this year."