The vote had been scheduled for Sunday. This is the latest of several delays in the election originally scheduled for late 2016, amid opposition concerns that President Joseph Kabila had been looking for ways to stay in power. Kabila, in office since 2001, earlier this year announced he would step aside.
After last week's fire destroyed some 8,000 voting machines in Kinshasa, officials found replacement machines but had to get 5 million new ballots printed and prepared, said Corneille Nangaa, head of the national electoral commission.
He called on the country of some 40 million voters for calm. The delay of even a week could spark another wave of unrest. Some protesters quickly gathered outside the electoral commission's offices to demonstrate against the decision to postpone the vote.
"Nangaa speaks nonsense. They didn't organize the election in seven years and they want us to believe they will be ready in seven days? Kabila is sabotaging the election. Kabila must go," said Fiston Adumba, 32.
Tensions have been rising in Congo, which has not had a peaceful, democratic change of leader since it became independent from Belgium in 1960. On Wednesday the governor of Kinshasa, Andre Kimbuta, banned all election rallies in the capital, citing security concerns. That prevented opposition leader Martin Fayulu from holding a rally. Thousands of angry supporters gathered but police dispersed them with tear gas.
"No postponement is justifiable," Fayulu's coalition said in a statement late Thursday, saying it would not accept the delay and accusing Kabila of trying to stay in power and "continue to loot the country."
"For us, it's a decision that bothers us ... but we bow to it," Kikaya Bin Karubi, Kabila's special adviser and a spokesman for ruling party candidate Emmanuel Ramazani Shadary, told The Associated Press.
Several people have been killed in recent days at chaotic opposition rallies in various parts of the country, leading the U.N. Security Council to issue a statement this week calling on Congo's government to "swiftly investigate." The council also called for a "violence-free environment."
On Dec. 12, the U.N.'s special representative in Congo denounced "the obstacles encountered by some opposition candidates during their efforts to hold public meetings in certain cities around the country." Among several incidents, Fayulu was prevented from landing in Kindu where he was scheduled hold a rally on Dec. 9, according to his campaign manager, Pierre Lumbi.
"I am concerned by the growing tensions ... and the risk of escalating violence that could lead to the commission of grave crimes," the prosecutor for the International Criminal Court, Fatou Bensouda, said in a statement on Thursday. She warned that anyone who "incites or participates in mass violence" could be prosecuted.
Other observers have expressed concern over whether adequate election materials have been distributed across the vast country that is more than three times the size of Texas. Congo is using voting machines for the first time, a rarity in Africa, and opposition members, diplomats and technical experts have expressed concern about the possibility of manipulation.
Associated Press writer Mike Corder in Amsterdam contributed.
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