At least 15 people have been killed and dozens of others injured during two days of demonstrations in Congo's east against the United Nations mission in the country, officials said Tuesday.

The United Nations confirmed that one peacekeeper and two international officers serving with the UN peacekeeping force were killed and another injured at the UN base in Butembo in North Kivu province in the east when "violent attackers snatched weapons from Congolese police" and fired on the UN personnel.

UN deputy spokesperson Farhan Haq said reports of civilian casualties, including reports of UN peacekeepers killing and injuring civilians, would be investigated.

He said that on Tuesday "hundreds of assailants again attacked bases of the UN force, known by its French acronym MONUSCO, in Goma as well as other parts of North Kivu "fuelled by hostile remarks and threats made by individuals and groups against the UN, particularly on social media."

"Mobs are throwing stones and petrol bombs, breaking into bases, looting and vandalizing, and setting facilities on fire," Haq said. "We are trying to calm things down" including by dispatching quick reaction forces but there is no evidence the violence has ended.

In addition, Haq said at least four incidents targeted the residences of MONUSCO staff, who have now been relocated to UN camps. And a mob also tried to enter the compound of the UN Development Program earlier Tuesday but was rebelled by security guards, he said.

Demonstrators on Monday had set fires and forced entry into the UN mission offices in Goma, accusing the peacekeeping forces of failing to protect civilians amid rising violence in Congo's eastern region. They are calling for the UN forces, present in Congo for years, to leave.

Congo's police said at least six people were killed in Goma on Monday, and eight civilians in Butembo.

Earlier, government spokesperson Patrick Muyaya said at least five people were killed and about 50 wounded by Monday.

Protesters blamed shots fired by the peacekeepers for the deaths.

Escalating violence

Congo's mineral-rich east is home to myriad rebel groups and the region's security has worsened despite a year of emergency operations by a joint force of the armies of Congo and Uganda. Civilians in the east have also had to deal with violence from jihadi rebels linked to the Islamic State group.

The government spokesperson didn't say what caused the deaths but described the response by security forces and peacekeepers as "warning shots to disperse the demonstrators and prevent any attack on the @MONUSCO base and installations," he said on his Twitter account.

"The government has instructed the security forces to take all measures to ensure a return to calm and the normal resumption of activities in Goma," he said. He also reiterated that steps are already being taken for the peacekeeping forces to be withdrawn.

Within that, he said, the UN has been "doing our best" to ensure that people's lives and basic freedoms aren't taken away.