UN troops helped the army retake Mbandaka airport
The Democratic Republic of Congo army killed at least 11 civilians as it retook the airport in Mbandaka from rebels this month, a rights group says.
The Asadho campaign group says it has confirmed 11 killings but suspects another 31 during the Easter attack.
Nine of the dead had been in detention for three months but were then accused of being rebels and killed, it said. The government is investigating.
The attack, which followed clashes over fishing rights, left two UN staff dead.
DR Congo's army has a reputation for brutality and stealing from and raping the people it is supposed to protect.
Thousands of former rebel fighters have joined the army under various peace deals.
The dispute in Mbandaka is separate from the unrest involving numerous armed groups in eastern DR Congo, which has drawn the world's biggest peacekeeping operation to the country.
Names of dead
UN peacekeepers helped the army retake control of the airport in the north-western Equateur province on 5 April.
The government has accused UN peacekeepers of not helping a shipowner in Mbandaka who was killed by the rebels.
Government spokesman Lambert Mende said it was the first time he had reports of army killings in Mbandaka.
"If Asadho gives the names of the people executed it will be easy for us to investigate further. So yes, we will open an investigation on this," he told the BBC.
Asadho says it does have these names.
Several Congolese soldiers are currently facing charges at a military court in Mbandaka - some are charged with looting, some are charged for failing to counterattack and running away from the enemy.
One officer has already been condemned to death as he was accused of having looted UN premises at Mbandaka airport.
Another three have been sentenced to jail terms, according to Asadho.
An unknown number of rebels are also facing trial.
Mbandaka is the capital of Equateur province, where at least 100 people were killed in clashes between the Lobala and Boba communities last year, displacing an estimated 200,000 people.
The rebels were thought to be from the Enyele community - a Lobala sub-tribe.