Local mayor Edmond Masumbuko on Sunday said 42 people had died in Saturday night's mass killing in Beni
Civil society groups in the Democratic Republic of Congo on Monday said the number of people hacked to death in the restive east this weekend has risen to 51.
"Our team on the ground has counted 51 bodies slain with machetes," said Teddy Kataliko, a member of a local alliance of NGOs and unions working in the troubled town of Beni.
Local mayor Edmond Masumbuko on Sunday said 42 people had died in Saturday night's mass killing in Beni; the government in Kinshasa had earlier put the death toll at 36.
Government spokesman Lambert Mende said the civil society groups' toll was "impossible to objectively verify".
Saturday night's attack was the latest in a string of killings that have left more than 650 people dead in and around Beni since 2014.
The army has blamed the attack on the Allied Democratic Forces (ADF), a partly Islamist armed group of Ugandan origin.
The group has been present in DR Congo for more than two decades and is accused of copious human rights abuses.
The killings sparked rage among local residents who accused the government of failing to protect them.
Some of the victims' families refused to take their relatives' bodies to the morgue, Kataliko told AFP.
"They decided to hold private funerals and refused to allow the government to bury them, because it could not guarantee their security while they were still alive," he added.
All shops were shut in Beni on Monday and the streets plunged into silence for the first of three days of national mourning.
- Kabila visit -
The attack took place just three days after a visit by President Joseph Kabila to the area.
On Monday Kabila was in the regional capital Goma for a meeting of security officials, and he was later due to visit Beni.
Army spokesman Mak Hakuzay told AFP that military units deployed in the area would be given new uniforms, because ADF rebels "have infiltrated" an area under the Congolese armed forces' control.
The ADF, opposed to Uganda's President Yoweri Museveni, is thought to be deeply embroiled in criminal networks funded by kidnappings, smuggling and logging.
Despite efforts by the international community and the Congolese authorities, the region has remained mired in violence since the end of the second Congolese war (1998-2003).
A report published in March by the Congo Research Group at New York University, which looked into the massacres around Beni, claimed that soldiers from the regular army had also participated in the killings.