With heavily-armed United Nations patrols and a rapid-reaction force of European troops in Kinshasa, members of the opposition are accusing other nations of trying to keep Joseph Kabila, president of the DRC, in office.
"Some people in the international community are trying to make Kabila win in the first round," third-placed candidate Oscar Kashala told Reuters late on Thursday.
"If that happens there will be blood on the streets," he said
Speculation over foreign meddling was heightened in mid-June when EU aid commissioner Louis Michel referred to Kabila as the "hope" for Congo - just one of several comments by the former Belgian foreign minister which stirred anger in Kinshasa.
Kabila is favourite to win Sunday's vote thanks to strong support in the densely populated east. But analysts say if he fails to win a majority and the election goes to a second round on Oct 29, an opposition alliance might force him from power.
"Europeans think we Congolese will accept anything, but one day there will be a nationalist backlash. We are going to start killing white people"
Joe, a Congolese businessman
Supporters of Kabila's main rival, former rebel leader Jean-Pierre Bemba, the interim vice-president, adopted anti-foreigner slogans and threatened journalists at a protest last week.
"There are some [foreign] actors here who are completely partial," Bemba told journalists this week, saying outside meddling was stoking xenophobic sentiment.
"The Belgian ambassador is really the one to campaign for Kabila publicly. Be careful! Congo's new leader must come from us," he said.
Belgian Ambassador Johann Swinnen has said publicly his country does not have any partisan position at the polls.
Despite relatively orderly voting on Sunday, chaos in Kinshasa counting centres has renewed fears of manipulation. A mysterious fire burned piles of ballots at one major centre in an opposition district of the capital on Thursday.
Sheets of paper showing Bemba in the lead are circulating in Kinshasa, where many regard Kabila as an eastern "foreigner".
"If Kabila wins, especially in the first round, there will be accusations that 'you stole the election from us'," said Jason Stearns, analyst at International Crisis Group think tank.
European election observers in Kinshasa reported hostility from Bemba supporters on Sunday. Convoys of European troops have been stoned in the streets and an unmanned Belgian surveillance plane was brought down by small arms fire last week.
Demonstrators in Kinshasa
protested outside involvement
"Europeans think we Congolese will accept anything, but one day there will be a nationalist backlash. We are going to start killing white people," said Joe, a 34-year-old businessman.