Pope Francis returned to Rome Monday after the first papal voyage to Mongolia, expressing admiration for its people and those of neighbour China while acknowledging such trips were getting harder to make.

The 86-year-old ventured to the vast, isolated Central Asian nation as a gesture of support to its tiny Catholic community, but the trip was overshadowed by apparent overtures to Beijing, with whom the Vatican for years has struggled to make inroads.

"Relations with China are very respectful, very. I have a great admiration for the Chinese people," the pope told reporters on his flight home.

He added: "I think we need to go further on the religious side to understand each other better. 

"So Chinese citizens don't think that the Church doesn't accept their own culture, their own values and that the Church represents another foreign power."

Francis had made a similar point earlier, telling a group of missionaries Saturday in Mongolia capital Ulaanbaatar that governments had "nothing to fear" from the Catholic Church, in a statement widely seen as a reassurance to China.

He also directly addressed the Chinese people -- some of whom were in the congregation of a Sunday mass, on pilgrimages unauthorised by Beijing -- telling them to be "good Christians and good citizens".

Francis, in the 11th year of his papacy, is anxious to make inroads for the Catholic Church in China, where a contentious 2018 deal renewed last year both Beijing and the Vatican a voice in choosing cardinals.

But an invitation to visit from Beijing is yet to arrive, and Francis on Monday suggested, as he ended the 43rd voyage of his papacy, that future trips could be limited. 

"I'll tell you the truth, for me taking a trip now, it's not as easy as in the beginning, there are limitations, in walking," he said, when asked what official visits he envisioned.

The pope underwent a hernia operation in June and knee pain forces him to rely on a wheelchair or cane. While in Mongolia, he walked unsteadily and often looked tired. 

- 'Dear Pope' -

Mongolia, a young democracy since 1992 with freedom of religion enshrined in its constitution and a history of coexistence between religions, offered Francis an apt platform for an appeal for interfaith dialogue.

His gesture of support for its 1,400 Catholics also fulfilled his desire to reach out to often ignored areas far from Rome.

The Buddhist-majority former Soviet satellite state, sandwiched between China and Russia, counts just 25 Catholic priests -- only two of them Mongolian.

"Dear brothers and sisters of Mongolia, thank you for the gift of friendship that I received in these days. Bayarlalaa ('Thank you', in Mongolian)! May God bless you," the pope's X account, formerly Twitter, said soon after his departure. 

Earlier Monday, during the pope's visit to a homeless shelter and clinic in the outskirts of the capital, a group of women from mainland China sang in Mandarin, wiping away tears as the pope's black car passed.  

"Dear Pope, our best wishes for you," they sang.

Many Chinese Catholics who came to see the pope told authorities at home they were travelling to Mongolia for tourism, according to interviews with AFP.

- 'Not against our country' -

China's government, which is officially atheist, is wary of the Catholic Church on its territory, and exercises strict control over all recognised religious institutions.

A Chinese woman from the northwestern city of Xi'an who attended mass Sunday described to AFP the difficulty of making the pilgrimage, saying two organisers of her tour had been detained back in China. 

"Let me tell you, I feel so ashamed to hold the (Chinese) national flag," she said. 

Another woman in the congregation from the Chinese province of Hebei told AFP that "to have our own religion doesn't mean that we are against our country", she added.

Mongolia has sought to toe a neutral line with its neighbours Russia and China, on whom it depends for imports of energy and the export of its coal, even as it reaches out to third countries, including the United States and South Korea, for balance. 

Francis called himself a "pilgrim of friendship" during his trip to Ulaanbaatar, extolling Mongolia's virtues while warning of the dangers of corruption and environmental degradation.

Mongolia has been marred by corruption and environmental degradation in recent years, with its capital suffering from some of the world's worst air quality and an embezzlement scandal sparking street protests last year.

Vast swathes of the country are also at risk of desertification due to climate change, overgrazing and mining.

ams/ar/giv