A police spokesman quoted by the Guardian on Sunday said four people had been killed in clashes with security forces in the capital, Kinshasa, and three of the deaths were being investigated.
Catholic churches and activists had called for peaceful demonstrations after Sunday mass, one year after they oversaw the signing of an accord that set a new election date to ease tensions in the mineral-rich country.
Kabila, whose mandate ended in December 2016, had agreed to set an election date by the end of 2017. Congo's election commission says the vote cannot be held until December 2018. Critics accuse Kabila of postponing elections to maintain his grip on power, causing tensions to increase and provoking violence and deadly street demonstrations across the country since the end of 2016.
The United Nations Human Rights office in D.R. Congo has condemned the use of force against peaceful demonstrators and the violent suppression of fundamental rights by security forces. More than 100 protesters have been detained so far by the police.
Congo's election commission has set a new date for presidential and legislative elections, which is to be held on December 23, 2018, though the opposition has said it would only agree to delay the vote until June 2018.
Kabila can remain in power until the next election is held, although he is barred by the constitution from seeking another term in office. (ANI)