Pressure is growing on the electoral commission of the Democratic Republic of the Congo to release the results of last week’s election on time after the Catholic church said there was a clear winner and it knew who had been elected the next president.

The US state department, the African Union and the Catholic church, which wields significant power in the central African country, have all urged the country’s government to respect the result.

Opposition members fear the election may be rigged in favour of Emmanuel Ramazani Shadary, the ruling party candidate who was handpicked by the current president, Joseph Kabila.

Q&A Why is the DRC election so important? Show The Democratic Republic of the Congo's sheer size, its political history and its myriad problems are all reasons why observers have followed its election so closely. The vast, resource-rich country, with a population of 80 million spread over an area the size of western Europe, has never known a peaceful transition of power since its independence from Belgium in 1960. It remains one of the poorest places in the world, racked by war and disease and with massive inequality. In the east, where scores of militia commanders battle for control of mines, an outbreak of Ebola has killed more than 300. Countrywide an estimated 4.3 million people are displaced. It is still recovering from a civil war triggered by the fall of the dictator Mobutu Sese Seko in 1997, in which 4 million people died. Joseph Kabila has been in power as president since his father, Laurent-Désiré Kabila, the victor of that conflict, was shot dead in 2001. The country’s problems have been exacerbated by the refusal of Kabila to leave power after the end of his second mandate two years ago, which is why December’s much-delayed election was invested with so much hope and trepidation. Chaos at polling stations on the day of the vote dampened hopes that the election would bring a measure of political stability. The announcement by the electoral commission on 10 January that Felix Tshisekedi had won confounded polling that had put another opposition figure well in front and raised fears of a backroom deal ultimately keeping Kabila in power. Photograph: Stefan Kleinowitz/EPA

The Catholic church, which sent more than 40,000 observers to polling stations across the country, said it knew who the winner was, urging the national electoral commission (CENI) to publish the result.

It stopped short of giving the winner’s name, as this is illegal in the DRC, but several observers said it signalled that Shadary had lost.

“We call on the CENI, as an institution supporting democracy, to respect truth and justice, taking full responsibility as it publishes election results,” the national episcopal conference of Congo (Cenco) said in a statement.

The results of the election on 30 December are due on Sunday, but the electoral commission has indicated that delays are likely.

The government has cut internet access and blocked SMS messaging, as well as blocking the signals of two broadcasters and withdrawing a French correspondent’s accreditation, in what Angela Quintal, of the Committee to Protect Journalists, called a “systematic campaign of censorship”.

The government hit back at the allegations. “Stop intimidating us,” Congolese media reported the electoral commission head, Corneille Nangaa, as saying. “Stop trying to influence the CENI decision. The CENI will announce the results in accordance with the law and the results it collected in all polling stations.”

Lambert Mende, the minister of communications, defended the internet shutdown and the revocation of the accreditation of the Radio France International correspondent. He said: “We’re not a sort of zoo in which thrill-seeking tourists from the whole world are invited by pyromaniacs to see savages fighting in a lawless land.”

President Kabila’s mandate expired in 2016 but he delayed elections by more than two years, arguing that an important census had not yet been held to count the number of voters, and that the country could not find the £1.4bn it said it needed to hold an election. He has ruled the country since 2001, when his father was assassinated.

Polling just before the election showed a large majority of Congolese supported the opposition candidate, Martin Fayulu, a former businessman.

The same poll showed almost half of respondents said they would protest against a rigged election, and more than half said they would not accept the result if Shadary was declared the winner.

The US threatened sanctions against officials attempting to undermine democracy.

Robert Palladino, a state department spokesman, said: “Those responsible for undermining democratic institutions and processes, threatening the peace, security, or stability of DRC or benefiting from corruption ‎will be held accountable.

“Those who undermine the democratic process, threaten the peace, security or stability of the DRC, or benefit from corruption may find themselves not welcome in the United States and cut off from the US financial system. There are moments in every nation’s history when individuals and political leaders step forward and do the right thing. This is one of those moments for the DRC.”

Jason Stearns, the director of the Congo Research Group at New York university, said the DRC was “in a different universe” after the church’s statement.

“I think it is a very crucial moment,” he said. “I don’t think Kabila’s going to step down tomorrow ... but we had always suspected there were going to be flaws in the electoral process, there were certainly many suspicions that they could be rigged in favour of the ruling coalition but to have the Catholic church step up and say we know who won these elections, we have proof and we will publish – that is very different from just saying the process has been flawed.”

He added: “They’re trying to make sure we don’t end up in a situation where CENI announces different results, there are then inevitable protests in the streets that turn violent, there’s a regime that digs in its heels and they end up in an ugly confrontation. To be honest, that’s where I think we’re going to end up.”

Perhaps only way it wouldn’t, he said, was if the South African and Angolan presidents, the African Union chair and Mike Pompeo, the US secretary of state, all got together and told Kabila: “It’s over, it’s over, it’s over, step down or else.”

That is unlikely – Kabila is in a powerful position, as the DRC is the largest copper producer in Africa and produces 60% of the world’s cobalt, which is used in lithium-ion batteries for smartphones and electric cars.