The Democratic Republic of Congo announced on Sunday that the much delayed elections to replace President Joseph Kabila would take place in December 2018, but the opposition demanded the long-time leader step down sooner.
Elections were due to take place this year under a deal whereby Kabila would leave office but repeated wrangling has hobbled the process.
The election commission said "direct voting" will take place on December 23, 2018, covering presidential, legislative, regional and local elections, said Independent National Electoral Commission (CENI) official Jean-Pierre Kalamba.
But the Congolese opposition said the time frame was not acceptable, insisting that Kabila quits by the end of this year.
"We reject the (CENI) calendar... what interests us right now is the departure of Kabila by December 31, 2017," said Augustin Kabuya, spokesman for the main opposition Union for Democracy and Social Progress (UDPS).
The electoral commission said provisional results of the presidential election would not be published until a week after the voting, on December 30, 2018, with definitive results not issued until January 9, 2019.
The new president will then take office on January 12, 2019, CENI said.
That calendar is based on "rationalisation of the electoral system so as to reduce the costs," said CENI chief Corneille Nangaa.
But senior opposition figure Moise Katumbi dismissed the plan.
"This predatory regime wants to prolong the instability and misery of the people," Katumbi said.
"We do not accept this fantasy calendar. Stop. Kabila must go," he tweeted, demanding a transitional administration without Kabila with elections in January.
Tensions have been running high in the central African nation of DR Congo since Kabila failed to step down on the expiry of his second and final term last December.
The electoral commission had previously said that there would be no vote before early 2019, mainly because of the problems of completing an electoral roll in the troubled central region of Kasai.
Sunday's announcement came 10 days after a visit by US ambassador to the United Nations Nikki Haley, who called for DR Congo elections next year.
"This calendar was drawn up under pressure from the international community and Congolese civil society," said Nangaa.
Britain, France, the EU and the UN, as well as Washington, had been among those calling for months for an announcement on election dates.
Haley, in a stark message during her visit to Kinshasa, said that "for every day which goes by without holding elections, a woman is raped, a child has an unwanted pregnancy [and] children are inducted by armed groups".
Uncertainty has bred fear of a new eruption of political violence in a vast, poor country already battling with ethnic divisions and violence in its east.
Demonstrations have been banned or widely repressed since September 2016.