Catholic churches and activists had called for the New Year's Eve protests against President Joseph Kabila's refusal to step down. The United States and others have condemned Congolese security forces' response to the protests at more than 160 churches, which included tear gas in churches and the arrests of altar boys.
The United Nations has said Congolese security forces killed at least seven people in those protests, which came one year after the Catholic church oversaw the signing of an accord that set a new election date to ease tensions in the vast, mineral-rich Central African country.
Kabila, whose mandate ended in December 2016, had agreed to set an election by the end of 2017. But Congo's election commission later said the vote cannot be held until December 2018.
Critics accuse Kabila of postponing elections to maintain his grip on power, while international observers have warned that the political tensions could further destabilize the impoverished country and the region at large.
The mourners on Friday fled the cathedral during the mass led by Laurent Monsengwo Pasinya, the archbishop of Kinshasa. They had cheered his call for "the right to demonstrate peacefully."
"What is Kabila's plan? It's to organize elections unilaterally and through them to push forward" his political heir, said opposition activist Mike Mukebayi Nkoso. "His successor will organize a constitutional referendum six months after elections, and once the constitution has been changed Kabila will have the chance to get back to business. That's what we face.
"So we need to stand as the church is standing, stand up together behind the church to block this Machiavellian scheme."
Congo's ambassador to the U.N., Ignace Gata Mavita, played down the New Year's Eve clashes during an appearance before the U.N Security Council earlier this week and insisted there had been no deaths linked to the unauthorized demonstrations.
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