The Antonov transport plane had just taken off and had "several dozen people" on board, an airport source told AFP, speaking on condition of anonymity.
The plane went down in Nsele, about 100 kms to the east of Kinshasa, capital of the Democratic Republic of Congo, the source said.
A local official in the area of the crash told AFP there were "no survivors".
The plane, which had a Russian crew, was carrying "two vehicles and weapons" and military personnel, a source at the army's headquarters told AFP, also speaking on condition of anonymity.
A witness at the crash site told AFP he had seen the plane "falling" out the sky shortly before 9:00 am but said there was no sign of any smoke coming from the aircraft.
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