The results of last month's disputed presidential election in the Democratic Republic of Congo were "mismanaged" and lack credibility, according to a team of international election observers.

The vote, which resulted in the re-election of President Joseph Kabila, was plagued with wide variations in the quality of vote counting, The US-based Carter Center said.

Multiple locations around the country reported nearly 100 percent voter turnout, with most or all of the votes going to the incumbent president. And there was evidence that results from nearly 2,000 polling stations in the capital, Kinshasa, disappeared, the Carter Center said in a statement released late Saturday. 40 percent of the 169 compilation centers around the country received a "poor" rating from the center.

Congo's electoral commission declared Friday that Mr. Kabila was the winner of the November 28 poll. Mr. Kabila's loyal Republican Guard has recently fired upon unarmed opposition supporters, resulting in the deaths of at least 18 people over the weekend prior to voting. Three people were allegedly killed by police on Thursday.

Kabila's main challenger, long-time opposition leader and former prime minister Etienne Tshisekedi, said the results are "totally unacceptable". Prior to the elections, he told supporters to "take responsibility" for the outcome if he judged that the vote had been stolen. Tshisekedi has rejected the results and declared himself president.

These were the second round of elections in the Democratic Republic of Congo since the fall of Mobutu Sese Seko's dictatorship and a civil war in the late 1990s and early 2000s that killed as many as 5 million Congolese.