The United Nations is urging calm in the Democratic Republic of Congo after European observers described widespread voting irregularities in this week's presidential and parliamentary election.

U.N. mission chief Roger Meece said Thursday he is concerned about the reports of irregularities, but stressed that any grievances should be addressed through peaceful means.

A preliminary European Union report says election observers saw ballot box stuffing, ballot shortages, and said some people were turned away from the polls.

Witnesses also say they saw thousands of plastic bags with ballots piled up in a parking lot in Kinshasa. They say ballots blew away and others were soaked by rain when some of the bags broke open.

An official with Congo's Independent National Election Commission told VOA the reports are “exaggerated.”

President Joseph Kabila is running for re-election against 10 challengers, three of whom have called for the vote to be annulled.

A fourth opposition candidate, Vital Kamerhe, has withdrawn his call for annulment, saying voting conditions improved as the election went on.

Vital Kamerhe, opposition leader, “My position is clear. My people and my nation pass before my ambitions. It's first Congolese, our nation. I refuse war in our country.”))

Meanwhile, Congo's government says it is bracing for possible clashes if the results are officially contested. Security minister Adolphe Lumanu says his forces are prepared for a post-election dispute.

Adolphe Lumanu, Interior and Security Vice Prime Minister: “We have a plan to provide security during the electoral process. While we were preparing for the elections, we knew that there were those who were getting ready to contest the elections. I think that we are sufficiently prepared, we have a well trained and equipped police force, we are ready to face the situation, today, tomorrow and after the elections.”))

The U.N. says it is investigating claims that more than 10 people were killed by security forces and supporters of political parties since last Saturday.

African Union and other African observers have said the election was successful despite logistical problems.

U.S.-based monitors from the Carter Center reported a range of irregularities and logistical problems.

The election was originally set to last one day but stretched into three because of irregularities.

Final results of the presidential vote are expected before President Kabila's term expires on December 6, while parliamentary results are not expected until January.