Updated

The U.N. peacekeeping chief condemned "violent repression" by Congo security forces against demonstrators protesting the refusal of President Joseph Kabila to step down and warned Tuesday that further electoral delays risk fueling political tensions.

Jean-Pierre Lacroix told the Security Council that "the crisis of legitimacy" for Congo's institutions and a lack of progress toward implementing a 2016 electoral agreement fueled "frustrations, impatience and tensions that led to violence" on New Years' Eve.

Priests and activists had called for peaceful demonstrations after Mass on Dec. 31, one year after the Roman Catholic Church oversaw the signing of the accord that set a new election date to ease tensions in the mineral-rich country. More than 160 churches participated in the demonstrations.

Kabila, whose mandate ended in December 2016, agreed to set an election by the end of 2017, but Congo's election commission said the vote couldn't be held until December 2018.

The U.N. Mission in Congo and police have said security forces killed at least seven people and at least one policeman died in violence during the protests by more than a thousand people in the capital of Kinshasa.

The U.S. ambassador to the United Nations, Nikki Haley, said the excessive force by government security forces included using live ammunition against protesters and tear gas inside churches and arresting civilians including altar boys.

"To hear reports of such brutality and cruelty against innocent civilians and children in the most sacred of places is truly horrifying," she said in a statement.

Lacroix and Haley urged Congo's government to hold security forces accountable for the violence.

Congolese Ambassador Ignace Gata Mavita played down the clashes and insisted there were no deaths linked to the unauthorized demonstrations.

He told the council there were five violent deaths throughout the country Dec. 31 — two thieves, a "terrorist" on a wanted list, a police officer "killed by terrorists" and "an unidentified terrorist" killed in a clash with security forces in volatile Kasai.

Gata Mavita said Kabila underscored on Dec. 31 that authorities are determined to hold elections on Dec. 23, 2018.

"The right attitude of all political actors and all Congolese people should be to do everything possible to prepare for the smooth holding of these elections in a peaceful manner," Gata Mavita said. "It is not normal to see the kind of unrest and organization of demonstrations that were at the heart of the events that took place on Dec. 31."

Critics accuse Kabila of postponing elections to maintain his grip on power, which has caused tensions to increase and provoked violence and deadly street demonstrations across the country since the end of 2016.

Lacroix, the peacekeeping chief, warned that "further delays in the electoral process not only risk fueling political tensions but also compounding an already fragile security situation."

He said it is imperative that Congo's political leaders adhere to the constitution, the 2016 political agreement and the electoral calendar.

"Political brinkmanship and a refusal to compromise will only result in further delays and deepening of the political crisis," he said.

The Security Council also underscored the importance of implementing the political agreement and urged the government to abide by the electoral calendar.