At least 34 people have died, after IS-backed rebels launched a brutal attack on a church in Goma.
The Associated Press in Central Africa also reports that five others were killed in Machongani, a nearby village.
Gunmen attacked the Catholic church in Komanda, killing dozens before burning shops and houses.
A local civil society leader said: “We are truly disappointed because it is incredible that such a situation could occur in a town where all the security officials are present… We demand military intervention as soon as possible, since we are told the enemy is still near our town.”
Christians in Eastern Congo have suffered increased persecution in recent years, largely from Rwandan-backed M23 rebels as well as the Allied Democratic Forces (ADF), which began as a band of ideologically driven Ugandan groups but is now backed by the Islamic State.
Many are internally displaced, with churches being a key source of shelter for those who have left their homes.
Anti-persecution watchdog Open Doors ranks the Democratic Republic of Congo as the 35th most dangerous country to follow Jesus – despite over 95 per cent of the country identifying as Christian.