Moldovan intelligence officials say they have seized an "imposing quantity" of radioactive uranium from a criminal group and detained several people.

The Moldovan Intelligence and Security Service on Friday said the uranium was due to be sold for $210,000 but did not say how big the haul was.

In a statement, it said "a criminal group specializing in smuggling radioactive substances was uncovered."

It said there was an ongoing investigation into where the uranium came from and how the detained people got involved.

An Associated Press investigation revealed in 2015 that there have been at least four attempts in the past five years in which criminal networks with suspected Russian ties sought to sell radioactive material to extremists through Moldova.