Authorities in the Democratic Republic of Congo say they have dismantled an international network set up to illegally use uranium mined there.
Enriched uranium is used for nuclear power generation and weapons
Scientific Research Minister Sylvanus Mushi said DR Congo's top nuclear official and a colleague were being questioned in connection with the case.
The official, Fortunat Lumu, and the colleague were arrested on Tuesday.
The move comes amid reports that a large quantity of uranium has gone missing in recent years in DR Congo.
State prosecutor Tshimanga Mukeba earlier told the BBC that an "important quantity" of uranium was taken from the atomic energy centre in the capital, Kinshasa, without revealing any figures.
DR Congo's daily newspaper Le Phare on Wednesday reported that more than 100 bars of uranium, as well as an unknown quantity of uranium contained in helmet-shaped cases, had disappeared from the centre as part of a vast trafficking of the material going back years.
But the BBC's Kinshasa correspondent, Arnaud Zajtman, says that as of yet, no evidence has been made public to support the allegations made by the newspaper.
Mr Mushi said that "a vast network aimed at the fraudulent exploitation of DR Congo's uranium has been dismantled".
"It was a criminal network," he said, without giving any more details.
Referring to earlier reports that the two officials had been arrested on suspicion of uranium smuggling, Mr Mushi said that the prospection and exploitation of DR Congo's uranium had not yet started.
The UN's nuclear watchdog, the International Atomic Energy Agency (IAEA), has expressed concerns over the reports from DR Congo, saying it was investigating the situation.
Uranium is the basic raw material of both civilian and military nuclear programmes.
A mine in DR Congo's southern province of Katanga supplied the uranium that was used in the atomic bombs that were dropped by the Americans on the Japanese cities of Hiroshima and Nagasaki in 1945.
To thank and reward DR Congo, the Americans funded the creation of DR Congo's nuclear centre in 1958.
It was established on the university campus and only for research purpose.
But in the late 1970s, a bar of uranium disappeared from the centre, raising concern about security at the site.
Moreover, the site of the centre is facing some erosion problems. And people fear a landslide that could lead to a wider disaster, our reporter says.
In recent years, the IAEA has visited the centre and security was believed to have improved.