Fortunat Lumu, the director of the country's only nuclear center, and one of his aides were arrested Tuesday "because they were accused of having illicitly sold a quantity of uranium," Attorney General Tshimanga Mukendi said.
Mukendi refused to give information on the amount of uranium or the alleged buyer, saying those details were part of an investigation.
He added only that they were accused of orchestrating illicit contracts to produce and sell uranium.
National police representative Michel Kanka confirmed the arrest, but also refused to give details.
In August, Congo's government emphatically denied a report in The Sunday Times of London that a uranium shipment left its territory in 2005 bound for Iran, saying the dangerous element was tightly controlled by international agencies. Officials declined to say if there was any connection between the arrest and the alleged 2005 shipment.
The Sunday Times said the uranium was suspected of being extracted illegally from Congo's southeastern Shinkolobwe mine, which was closed in 1961.
Uranium can be used to breed plutonium, which is used both in nuclear warheads and as fuel for nuclear reactors. Lumu, as head of Congo's small nuclear reactor built for research just before Congo's 1960 independence, would likely have had access to the uranium, but it was unclear if in any large quantities.