The United States says the recent presidential election in the Democratic Republic of Congo was “seriously flawed.”

In a statement Wednesday, State Department spokeswoman Victoria Nuland said the U.S. assessment is based on reports from observation teams fielded by the U.S. and other embassies, as well as by independent election monitoring groups.

Nuland said it was not clear, however, whether the irregularities and lack of transparency were enough to change the outcome of the election.

She calls on Congolese authorities to conduct a “rapid technical review” of the electoral process which she says will help determine whether the irregularities resulted from poor organization or outright fraud. She said the U.S. is ready to give its “technical assistance,” for the review.

Congo's electoral commission declared President Joseph Kabila had won re-election, but challenger Etienne Tshisekedi has rejected the results and declared himself president.

Mr. Kabila has said there is no doubting the credibility of his re-election, and denied there was a crisis in Congo. He urged Mr. Tshisekedi to — in his words — “make good use of the justice system” if he disagrees with the election result.

Violent protests and looting left four people dead in Kinshasa following the announcement of the election results, but a heavy mobilization of police and security personnel has since restored a tense calm to the city.

Mr. Tshisekedi has called on supporters to remain calm and await further instructions. He has also expressed hope the international community will help mediate the dispute.

The presidential and legislative polls two weeks ago were only the second free elections since the African nation was torn apart by several years of warfare that ended in 2003.