Election observers and the opposition in the Democratic Republic of Congo say Sunday's presidential election was marred by widespread irregularities.

The Roman Catholic Church's observer team said it had received more than 500 reports of malfunctioning voting machines.

The opposition accused the military of trying to coerce people to vote for the ruling's party's candidate.

President Joseph Kabila insisted the election was free and fair.

BBC reporters in the capital Kinshasa and in the eastern cities of Goma and Lubumbashi say the internet has not been working since Monday morning.

Local observers, Symocel, have urged the government to turn the internet back on, saying it "sends the wrong message".

It is unclear whether the government has purposefully ordered the internet to be shut down. Telecoms minister Emery Okundji told the BBC he was unaware of the situation.

Mr Kabila is due to step down after 17 years in office, and has promised DR Congo's first orderly transfer of power since it gained independence from Belgium in 1960.

Counting is under way and provisional results are expected on 6 January.

Mr Kabila is backing his former interior minister Emmanuel Ramazani Shadary, who is the ruling's party's candidate.

The two main opposition candidates are Martin Fayulu, a former oil executive, and Felix Tshisekedi, the son of the late veteran opposition leader Etienne Tshisekedi.

What do observers say?
In its preliminary report on the poll, the 40,000-strong observer mission set up by the Catholic Church said there had been more than 100 cases of election monitors being denied access to polling stations.

It added that around 20% of polling stations opened late, and there were reports of polling stations being moved at the last minute.

About 40% of the population in DR Congo is Catholic, and Pope Francis had appealed for a peaceful vote.

Local observers Symocel say some of their 20,000 agents were subjected to intimidation and aggression.

They were particularly concerned with the lack of secrecy while people voted - reporting that only half the votes were conducted properly behind a booth.

What has been the opposition's reaction?
Mr Fayulu warned that the irregularities would have a negative impact on the electoral process.

In a BBC interview, he also accused the military of "pushing" voters in some areas to cast their ballots for Mr Shadary.

An internal UN report said armed rebels in eastern Masisi attempted to intimidate people to vote for Mr Shadary, reports the BBC's Louise Dewast from the capital, Kinshasa.

Mr Tshisekedi accused Mr Kabila's government of creating a "mess" on election day in order to trigger legal challenges that would help the president remain in power.

"I deplore all the disorder that we hear about," he said.

What's the context for these elections?
Mr Kabila took over from his assassinated father Laurent in 2001, but he was barred from running for another term under the constitution.

He was supposed to step down two years ago, but the election was postponed after the electoral commission said it needed more time to register voters.

The decision triggered violent clashes, as the opposition accused Mr Kabila of trying to cling on to power.

The run-up to the poll was also hit by controversy over the exclusion of some 1.26 million out of an electorate of nearly 40 million from voting.

The electoral commission said voting could not take place in the eastern cities of Beni and Butembo because of a deadly Ebola outbreak in the region. Voting was also called off in the western city of Yumbi because of insecurity there.

In some areas in the east where the poll was cancelled, activists organised their own election, dubbed "citizen votes".

They used ballot boxes from the 2011 elections and printed their own voting papers.

"We want to show the Ceni [electoral commission] that if they fail to organise elections here because of Ebola, we can do it," organiser Katembo Malikidogo told the BBC.

What do we know about the candidates?

There are 21 candidates, but three frontrunners:

Emmanuel Ramazani Shadary, a former interior minister and Kabila loyalist, who was hit by European Union sanctions for his role in the violent suppression of opposition protests in 2017
Martin Fayulu, a former oil executive who has promised "a dignified and prosperous Congo", but who poor Congolese feel may not advance their cause
Felix Tshisekedi Tshilombo, the son of a late veteran opposition leader who has promised to make the fight against poverty his priority