Police in the Democratic Republic of Congo (DRC) have blocked President Joseph Kabila's main rival at an airport in Kinshasa.
The authorities stopped Etienne Tshisekedi from staging an election rally after at least three people died in violence across DRC's capital city during campaign rallies.
The violence broke out when security forces used tear gas and live fire to disperse those attending campaign rallies.
Two days before presidential and parliamentary elections, rival factions hurled rocks at each other and gunfire was heard across town on Saturday.
'Live rounds and tear gas'
Al Jazeera's Yvonne Ndege, reporting from Kinshasa, said "thousands of supporters" had tear gas fired on them, adding that the "feeling among the opposition is that this is a sign of how popular the opposition are and that Kabila can't win Monday's elections".
Daniel Howden, Africa correspondent for the UK newspaper The Independent, said on Twitter: "Live rounds and tear gas" were being used "at large crowds in Kinshasa airport".
The violence was the latest sign of tension in the run-up to Congo's second election since a 1998-2003 war, a poll which has been marked by opposition allegations of irregularities and concerns about inadequate preparations.
Police stopped opposition leader Tshisekedi and his entourage from leaving Kinshasa's N'djili airport after his party said it would defy a ban on political rallies imposed earlier on Saturday.
After hours of failed negotiations by the United Nations peacekeeping mission, police moved in on Tshisekedi's entourage, dragging several people from their cars, according to a Reuters witness.
Tshisekedi was later escorted to his home by the police, according to a UN source.
Earlier, tens of thousands of Congolese turned out on the airport road, most of them identifiable as Tshisekedi supporters.
Some chanted his name while many billboards for Kabila and his allies had been torn down.
Kabila, Tshisekedi and the other main challenger, Vital Kamerhe, had been due to hold rallies within several hundred metres of each other in central Kinshasa on Saturday.
Under constitutional amendments signed off by Kabila this year, the presidential vote will be decided in a single round, meaning the winner can claim victory with a simple majority.
Analysts say that favours Kabila against the split opposition.
Despite a logistics operation supported by helicopters from South Africa and Angola, some observers doubt whether all the ballot slips will reach the 60,000 voting stations by Monday in a country two-thirds the size of the European Union.
However, national election commission president Daniel Ngoy Mulunda said he did not expect any delay to the polls, saying that materials were 90 per cent deployed in the provinces.
Kabila's rivals say fake polling stations have been set up to allow vote-rigging, an allegation denied by the authorities.
The opposition also accuses Kabila of using state media and transport assets for his campaign.
Kamerhe said the Congolese would not accept a rigged poll.
"They want free and fair elections that allow them to take their destiny in their own hands. People will refuse cheating wherever it takes place," he told Reuters, surrounded by chanting and dancing supporters at his party headquarters.
The UN Security Council, the European Union and other Western governments have all voiced concern at violence in the run-up to the vote and called for candidates to avoid stirring up their supporters with inflammatory rhetoric.