SIX people have been detained in Moldova for smuggling an unspecified amount of the form of uranium that can be used to make a nuclear weapon, an official says.

Interior Ministry official Vitalie Briceag said the uranium-235 was brought in from Russia.

In an indication that the amount was substantial, he said the smugglers were trying to sell it to “Muslim countries” for €20 million ($A27.42 million).

Uranium-235 makes up less than 1 per cent of natural uranium.

Highly enriched uranium – which is used to arm nuclear weapons – is 90 per cent or more uranium-235.

The International Atomic Energy Agency considers 25kg of uranium-235 a “significant quantity” – technical language for the amount needed to make a nuclear bomb.

IAEA officials contacted shortly after the detentions were reported said they had no immediate comment.

Four detainees are Moldovan citizens, one is Russian and another is from Moldova’s separatist Trans-Dniester region, said Briceag.

He said the uranium was kept in a lead cylinder, adding more information will be disclosed after an investigation is conducted outside the country.

In 2010, Moldovan authorities arrested three people who were trying to sell nearly two kg of uranium-238 worth €9 million ($A12.34 million) on the black market.