Tens of thousands Congolese gathered in the capital Sunday at an opposition rally calling for the president to step down at the end of his mandate in December, and urging elections take place as scheduled in November.

Many wore the blue, yellow and red colors of Congo's flag, and held signs that said "No to a third term."

Opposition leaders say President Joseph Kabila is delaying elections to remain in power. The constitutional court says he can stay in charge if elections are postponed.

Kabila's party has not designated another candidate, and he has not discussed plans for his political future.

"We are attached to our constitution, and it says that the president cannot go beyond two mandates," said main opposition party head Etienne Tshisekedi to the excited crowd. The popular leader returned to Congo last week after being away for two years for medical reasons. "If on Sept. 19 the electoral commission does not convene the electorate, we will talk of high treason."

Congo's electoral commission began voter registration Sunday in the northwest. The head of the commission, Corneille Nangaa, said this would lead Congo into elections, though has Nangaa said it will be difficult to organize the vote by Nov. 27.

The coalition of ruling parties held a rally Friday to support Kabila and a national dialogue in August.

Tshisekedi has said dialogue is needed, but the opposition will not participate with the African Union-appointed mediator, who he says supports Kabila. Opposition parties want international mediators and for political prisoners to be released, Tshisekedi said.

"We have campaigned for 30 years for democracy," he said, calling for no violence.

Junior Mutala, 26, was inspired. "This gives us hope for change," he said.