Pope Francis embarks Monday on a 12-day trip to Southeast Asia, the longest and farthest of his papacy that will challenge the 87-year-old's increasingly fragile health.

The pontiff will fly overnight and arrive on Tuesday in Jakarta, the capital of Indonesia, before heading to Papua New Guinea, East Timor and Singapore.

The distance covered -- some 32,000 kilometres (almost 20,000 miles) -- and time difference of up to eight hours would be enough to make a testing trip.

But Francis -- for whom spreading the faith is a priority -- will also deliver 16 speeches and hold several giant masses as he seeks to rally the region's growing Catholic community.

The trip -- his 45th abroad -- was originally planned for 2020 but postponed due to the Covid pandemic. And in those four years, the pontiff's health has suffered.

The Argentine now routinely uses a wheelchair to move around, underwent hernia surgery last year and has been plagued by respiratory issues. 

He has not travelled abroad since visiting Marseille in France in September 2023, having cancelled a planned address at United Nations climate talks in Dubai two months later.

But in recent weeks the pontiff has appeared in good spirits, and a Vatican source said that beyond the doctor and nurse who always travel with him, no special medical arrangements had been planned for this trip.

- Create communion -

The four countries on the tour are very different, but the pope will seek to bolster ties with each of their Catholic communities and their governments, observers say.

The goal is to "strengthen the sovereignty of the pope and the role of the Holy See with local Catholics, to create communion", said Michel Chambon, a theologian and anthropologist at the National University of Singapore. 

"If the Holy See wants to show its universality, it must rub shoulders with Asian traditions which, increasingly, play a major role in the international order," he told AFP.

Francis is also expected to address some of the key issues that have marked his 11 years as head of the Catholic Church, notably inter-religious dialogue, migration and the environment.

- Religious dialogue -

Francis will take most of the first day in Jakarta to recover from the flight, and the next day hold talks with outgoing President Joko Widodo, young people, diplomats and local clergy.

On September 5, he will meet representatives of all Indonesia's main religions at Istiqlal Mosque, the largest in Southeast Asia, and sign a joint declaration with the grand imam, Nasaruddin Umar.

Indonesia is the largest Muslim nation in the world but the country also officially recognises Protestantism, Catholicism, Buddhism, Hinduism and Confucianism.

Yet observers point to growing discrimination against religious minorities.

"Discrimination against the Christian minority in Indonesia remains a concern," Usman Hamid, executive director of Amnesty International in Indonesia, told AFP.

He said the situation varied widely depending on the region, but noted reports of attacks on churches and harassment of believers, as well as difficulties obtaining permits to build or renovate churches.

"Some congregations have been fighting for permits for decades," confirmed Krispurwana Cahyadi, a Jesuit priest and theologian who lives on the island of Java, which includes Jakarta.

"We still have problems with religious intolerance," he told AFP.

"Our country is not always as smooth as the ideals portrayed in the authorities' speeches."

Francis will be the third pope to visit Indonesia, an archipelago of 17,500 islands, after Paul VI in 1970 and John Paul II in 1989. 

East Timor sexual abuse

Francis heads on September 6 to Christian-majority, multi-ethnic Papua New Guinea, for a three-night visit during which he will meet with street children and make a day trip to Vanimo in the far northwest.

He is expected to repeat calls to protect the environment in a Pacific nation marked by deforestation and regularly struck by natural disasters.

Francis is then enthusiastically awaited in East Timor, one of the world's newest nations and the most Catholic of his tour.

Some 97 percent of the 1.3 million inhabitants are Catholic. But as elsewhere, the Church in East Timor has been hit by the global scourge of clerical child sex abuse.

In 2020, the Vatican sanctioned Nobel Peace Prize-winning Bishop Carlos Belo, who was accused of sexually abusing boys in East Timor over a 20-year period.

The pope's tour wraps up with a 48-hour visit to Singapore, a densely populated city-state of six million residents.