Security forces in the Democratic Republic of Congo carried out killings and arbitrary arrests after elections last year, according to a UN report.The UN Joint Human Rights Office documented the killing of 33 civilians in Kinshasa by members of the army, police and the elite Republican Guard.The country's justice minister has rejected the report's findings.International observers say last November's disputed elections, won by President Joseph Kabila, were flawed.The report focuses on the period between 26 November and 26 December 2011 in Kinshasa - seen as an opposition stronghold.It says that during this month, at least 33 people were killed - including 22 by gunshot - and at least 83 others were injured, including 61 who were shot.At least 16 people remain unaccounted for, it said.'Dumped in river'It said it had documented the arrest of at least 265 civilians, most of whom had been detained illegally or arbitrarily.Many of these, the report alleges, were detained due to their affiliation with the UDPS opposition party or because they came from the home province of its leader, Etienne Tshisekedi.It blames the bulk of these acts of violence on the Congolese Republican Guard and officers of the National Congolese Police and its specialised units.Witnesses are quoted as saying some of the bodies were dumped in the Congo river, while others were buried in mass graves.The report calls on the Congolese authorities to conduct independent investigations into all the cases of human rights violations committed in the capital to bring those guilty to justice.It also recommends that illegal detention facilities in the capital should be immediately shut down.The November elections were the first Congolese-organised polls since the end of a devastating war in 2003, which left some four million people dead.President Kabila has admitted that there were mistakes in the electoral process, but said no poll was 100% perfect and rejected concerns that the results, criticised by Western observers, lacked credibility.