The Democratic Republic of Congo's top atomic energy official is being held over allegations of uranium smuggling.
Enriched uranium is used for nuclear power generation and weapons
Atomic energy centre director Fortunat Lumu and an aide have been questioned since their arrest on Tuesday.
A large quantity of uranium is reported to have gone missing in recent years, although state prosecutor Tshimanga Mukeba did not reveal any figures.
He told the BBC an "important quantity" of uranium was taken from the nuclear centre and they were investigating.
DR Congo's daily newspaper Le Phare 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 nuclear centre in Kinshasa 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.
Creation of centre
Uranium is the basic raw material of both civilian and military nuclear programmes.
A mine in 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 town of Hiroshima in 1945.
To thank and reward Congo, the Americans funded the creation of 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 Vienna-based International Atomic Energy Agency has visited the centre and security was believed to have improved.
Last year, a partnership was also signed between Congo's atomic energy centre and British company Brinkley Mining, aiming at prospecting for uranium deposits in the Congo.
But our correspondent says that this new allegation of uranium smuggling might tarnish DR Congo's ability to handle dangerous and expansive products such as uranium and raise concerns about who might benefit.