The UN peacekeeping mission in the Democratic Republic of Congo is opening an investigation after gathering evidence that its troops may have killed a protester, a spokesman says.

The man died on Tuesday in the eastern city of Beni, where locals accuse the UN and government troops of failing to protect them from an Islamist militia.

The Allied Democratic Forces (ADF) have stepped up their attacks in response to a government offensive against them.

They have killed dozens of people.

The UN has an 18,000-strong force in DR Congo, but its troops and those of the government have struggled to curb instability in the mostly lawless east.

The ADF is one of many militia groups operating in eastern DR Congo, a mineral-rich area which borders Uganda and Rwanda. Formed by Ugandan rebels, the militia has been accused of widespread atrocities in the region.