Half way through his homily, Father Victor Ntambwe brandished his voter card in front of the congregation in Saint Charles Lwanga church in Democratic Republic of Congo's capital.

With presidential elections just months away, he had an earthly message to deliver alongside the psalms and the sermon. He told the worshippers to follow his lead, hold up their cards and show they had registered.

"If we do not register to vote, we will have the authorities we deserve, but if we enlist and vote, we can hold them to account," he told Reuters after Sunday's service.

Democratic Republic of Congo's Catholic church has a long history of promoting democracy in the vast African country where organising elections has been complicated by financial and logistical problems, and where disputes over vote tampering have frequently caused widespread unrest.

Once again, the church is gearing up to monitor elections scheduled for December in which President Felix Tshisekedi will seek a second term in office.

Preparations are underway just as Congo, home to 45 million Catholics - the most of any African country - prepares for the arrival next week of Pope Francis, the first papal visit since 1985.

In the decades since, Congo, whose vast mineral wealth has attracted investment from some of the world's largest companies, has been swept up in a myriad of simmering conflicts that have cost the lives of millions of people.

Amid the chaos, the Catholic church deployed thousands of observers across the country before and during voting. Sometimes, as was the case in the 2018 polls, its tallies - trusted by millions - have clashed with official results, raising concerns of fraud.

"The church has a duty to denounce what is wrong with society," Ntambwe said.