Authorities reported that during a second day of anti-U.N. rallies in the eastern Democratic Republic of Congo on Tuesday, three United Nations peacekeepers and at least 12 civilians were slain.

The rallies were sparked by concerns that the U.N. mission, MONUSCO, had not adequately shielded people from militia violence that had been raging for years.

U.N. Secretary-General Antonio Guterres condemned the violence, deputy U.N. spokesperson Farhan Haq said in a statement, adding, “He underscores that any attack directed against United Nations peacekeepers may constitute a war crime and calls upon the Congolese authorities to investigate these incidents and swiftly bring those responsible to justice.

Demonstrations began on Monday in the city of Goma and spread on Tuesday to Butembo, where a U.N. soldier and two U.N. police with the mission were shot dead, Haq told reporters in New York.

In both cities U.N. peacekeeping troops were accused of retaliating with force as hundreds of protesters threw rocks and petrol bombs, vandalized and set fire to U.N. buildings.

A Reuters reporter saw U.N. peacekeepers shoot dead two protesters in Goma, where government spokesman Patrick Muyaya said at least five people were killed and 50 wounded.

In Butembo at least seven civilians were killed and an unknown number wounded, said the city’s police chief Paul Ngoma.

U.N. peacekeeping missions have been beset by accusations of abuse for years.

“Obviously if there’s any responsibility by U.N. forces for any of the injuries, or any of the deaths, we will follow up on that,” Haq said.

U.N. forces were advised to use tear gas to disperse protesters and only fire warning shots if needed, he said.

The protests were called by a faction of the ruling party’s youth wing, which has demanded the U.N. mission withdraw over what it describes as its ineffectiveness.

Resurgent clashes between local troops and the M23 rebel group in eastern Congo in recent months have displaced thousands. Attacks by militants linked to Islamic State have also continued despite a year-long state of emergency and joint operations against them by the Congolese and Ugandan armies.

“We have been doing our utmost, not just for years, but really for decades to try to bring stability to Eastern Congo,” said Haq, adding that U.N. peacekeeping chief Jean-Pierre Lacroix is expected to travel to Congo as soon as he can.

MONUSCO took over from an earlier U.N. operation in 2010. MONUSCO had more than 12,000 troops and 1,600 police deployed as of November 2021, and has been gradually withdrawing for years.

Protesters also stormed the houses of U.N. workers in Goma, spurring the mission to relocate its staff to camps. A Reuters reporter saw staff being evacuated in a convoy with army escort.

India’s foreign minister said two of the peacekeepers who died were Indian. Ngoma said the third one was Moroccan.

The U.N. Security Council was briefed on the situation behind closed doors on Tuesday, diplomats said.