In a statement on Telegram, Islamic State said it was behind the attack.
Islamic State claimed responsibility on Tuesday for a deadly overnight attack in an area of eastern Congo hit by an Ebola epidemic, although its account of the violence differed from local reports.
The deputy mayor of Beni in the eastern Democratic of Congo said 13 civilians were killed late on Monday in an attack by the Allied Democratic Forces (ADF) - a group thought to be linked to Islamic State.
“The victims were killed by bullets and others by bladed weapons,” Mayor Modeste Bakwanamaha told Reuters.
In a statement on the messaging website Telegram, Islamic State said it was behind the attack.
It said it had targeted the Congolese army in Beni, killing or wounding 25 people.
The bloodshed added to widespread insecurity that has hampered efforts to contain the second-worst Ebola epidemic on record.
The number of cases hit 2,000 this week as the rate of infection accelerated.
Bakwanamaha said the latest violence was likely a response to a crackdown by the Congolese army last week that killed 26 ADF members after they attacked an army position in Ngite.
The ADF has never claimed allegiance to Islamic State, but Islamic State said last Thursday its ‘Central Africa Province’ affiliate had inflicted “dozens of casualties” on Congolese forces, according to the SITE Intelligence Group, which monitors online jihadist activity.