VATICAN CITY (AFP) - Pope Francis is gearing up for what is potentially his most politically charged trip yet, an eight-day whirlwind visit which will take him from Havana's Revolution Square in Cuba to the headquarters of the United Nations.
The Argentine, who will become the first pontiff to address a joint meeting of Congress in Washington, has taken advantage of a summer lull at the Vatican to fine-tune his hotly awaited speeches, sources at the Holy See say.
For his three-day visit to Cuba, beginning on Sept 19, Pope Francis can expect a warm reception from the Castro regime following recognition of the key role he played in Havana's reconciliation with the United States this year.
But anticipation ahead of the US leg of the trip, which will kick off in Washington on Sept 22, has already sparked conflicting reactions - as well as a boom in Pope Francis-themed souvenirs and trinkets.
The welcome from some American politicians is expected to be chilly. The 78-year-old's decision to visit Havana before Washington has not gone down well, particularly as Congress has yet to lift the embargo against Cuba.
His environmental encyclical and recent impassioned speeches in Latin America against the free market system, blind capitalism and rabid exploitation by multinationals of natural resources, have seen him accused of Marxism.
Asked in July how it felt to have been termed by one American television presenter "the most dangerous man on the planet", the pontiff merely replied that "every criticism must be received, studied, and then dialogue must ensue".
His speech to Congress will be a historic moment, and the outspoken pope will likely make no bones about the superpower's responsibilities in leading the way on tackling pollution and embracing renewable energy.
The fifth visit by a pope to the UN, dubbed the "Glass Palace", will see the Argentine hold forth on the social and ecological themes most dear to him, particularly ills such as the "culture of waste" and "globalisation of indifference".
Pope Francis is expected to urge member states to make concrete commitments at the Paris climate change summit in December. He is also likely to call for renewed efforts towards securing peace in the Middle East and greater dialogue with Islam, as well as insisting on the need to defend persecuted Christians around the world.
The fate of migrants, the plight of the poor and the scourge of human trafficking will likely be raised, and some conservatives fear he might weigh in on contentious political subjects, such as the Iran nuclear deal.
The Pope, a champion of the oppressed, is set to meet America's downtrodden, from homeless people to immigrant families, and will visit Ground Zero, the site of the Sept 11 attack.
Some feathers may be ruffled by his decision to canonise a Spanish Franciscan missionary, Junipero Serra, who was involved in converting to Christianity the native Indian population in California in the 18th century.
In Philadelphia, where he will arrive on Sept 26 for the closure of the 2015 World Meeting of Families, huge crowds are expected to gather to hear his message on marriage and the modern family.
The speech will come just one week ahead of a key Church meeting in Rome on the hot-button topic, which has raised hopes among liberals of an opening towards homosexuals and divorced people, but is unlikely to result in concrete change.
The Pope is supported by 87 per cent of American Catholics and 66 per cent of Americans, according to a recent survey. But he is decidedly out of favour with some US bishops, amid complaints he has not given them enough support against the Obama administration over abortion, contraception and gay marriage.