U.S. Ambassador Nikki Haley is urging the Security Council to use pressure if necessary to ensure that long-delayed presidential elections in Congo take place on Dec. 23.

She denounced the government's use of force against opposition demonstrators and demanded at an informal Security Council meeting Monday that Congo's government release political prisoners and guarantee freedom of expression and assembly.

Haley also warned that the electoral commission's decision to use an electronic voting system for the first time poses "enormous risk" and "has the potential to seriously undermine the credibility of elections." She said the U.S. won't support this system.

Electoral Commission President Corneille Nangaa said using voting machines that enable every voter to print a ballot before putting it into a ballot box will save $123 million in election costs.