Pope Francis urged Chinese Catholics to be "good citizens" and "good Christians," a rare instance of the Holy Father publicly addressing the issue of religion in China.

Francis' seemingly off-the-cuff comments came during his Sunday Mass in the Mongolian capital of Ulaanbaatar.

The trip has been scrutinized because of both its historic nature -- it is the the first ever by a Pope to the sparsely populated Asian nation -- but also because of its potential geopolitical reverberations. Mongolia is sandwiched between Russia, whose invasion of Ukraine Francis has publicly criticized, and China, an atheist state where religious practice is heavily curtailed by the government.

Officially there are about 6 million Catholics in China, but the number may be higher when counting those who practice at underground churches to avoid Beijing's watchful eye.

At the end of Mass, Pope Francis took the hands of the current Bishop of Hong Kong, cardinal-designate Stephen Chow, and his predecessor, Cardinal John Tong, calling them "brother bishops" before addressing China's Catholics

Francis said he wanted to take advantage of their presence at his Mass in Mongolia "to send a warm greeting to the noble Chinese people." Hong Kong's Catholic leaders play an important role in navigating Vatican-Beijing relations, as the territory allows its citizens greater freedom of religion than in mainland China.

"To the entire people I wish the best, go forward, always progress. And to the Chinese Catholics, I ask you to be good Christians and good citizens."

China may be officially an atheist state, but religious practice is legal in the country -- albeit under tight government supervision and surveillance.

Catholicism is one of five state-recognized faiths, but state-sanctioned Catholic churches were for decades by bishops chosen and ordained by Beijing, not the Holy See, until the two sides reached an agreement in 2018. Details of the accord have never been made public.

Francis landed in Mongolia Friday for a trip that has lacked the usual fanfare of a Papal visit.

There are only 1,500 Catholics in the entire country of 3.5 million, but that number has grown significantly in the decades following country's transformation from communist one-party rule to multiparty democracy in the 1990s. According to Vatican News, there were only 14 Catholics in the country in 1995.

The 86-year-old Pontiff spent the first day of his trip resting. He met with Mongolian political leaders on Saturday and on Sunday attended an inter-religious meeting alongside representatives from various religious communities, including Buddhists, Shamans, Muslim, Jews, and evangelicals and Russian Orthodox Christians.