The motive of the shooter was unclear, they said after the overnight attack in the city of Tshikapa in the Kasai region in the central DRC.
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"People were gathered to mourn when the soldier arrived and opened fire on the crowd killing two people on the spot and injuring others," a police source said.
Three of the wounded, including a soldier, died in hospital on Sunday.
A local journalist said that before opening fire the shooter demanded money from mourners.
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He was later arrested by military police, the journalist said, adding that tensions in the area were running high as families of the victims were seeking retribution.
Local authorities made no comment on the incident.
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