KINSHASA (Reuters) - Congo’s opposition leaders warned thousands of supporters at a rally in the capital Kinshasa on Saturday of what they say are moves by the government to steal the presidential election in December, when Joseph Kabila is due to step down after 17 years.

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The introduction of electronic voting and the authorities’ exclusion of a number of candidates from the ballot has united opposition parties ahead of the long-delayed vote on Dec. 23 that will choose a successor to Kabila.

Despite the suspension of all state public transport in the capital and the presence of heavily armed police, the rally site was thronged with supporters waving flags and hand-made signs with slogans such as ‘RIP voting machines.’

Addressing the crowd, Felix Tshisekedi, the president of Congo’s largest opposition party and a front-runner to replace Kabila, said opposition forces would remain united in the run-up to the election.

“No one will divide us. We will not cheat, anyone who cheats will provoke a scandal,” he said.

While united on some issues, opposition leaders have yet to coalesce behind a single candidate despite repeated promises to do so.

A key common concern relates to the introduction of tablet-style devices for voting, which some say are more vulnerable to vote-rigging and could be compromised by the unreliability of Congo’s power supply.

The authorities argue the system will cut costs, help reduce electoral fraud and accelerate the counting of votes in the vast central African country where past elections have been marred by voting irregularities or violence.

“They are not voting machines they are cheating machines,” opposition leader Jean-Pierre Bemba said via video-link from Brussels.

“They are not reliable, too slow and there are 10 million fake voters who have already been registered. We, the opposition, have united to say no to the machines,” he said.

Western governments and investors regard the vote as a crucial step towards ending political instability that is impeding investment in Congo, which is rich in natural resources but mired in poverty and economic and humanitarian crises.

But widespread voting irregularities would undermine what is hoped will be Congo’s first democratic change of power.

“We are ready for December 23 but we want fair and transparent elections. We do not want the voting machines, they are not ready to be used,” construction firm worker Eleck Tshibuabua,41, said on the sidelines of the rally.

On Tuesday, outgoing president Kabila told the annual U.N. gathering of world leaders that the election would be peaceful and credible.

Kabila has ruled since his father’s assassination in 2001. He agreed last month not to defy term limits by running for re-election, calming tensions following his refusal to step down when his constitutional mandate expired in December 2016.