The waste left the Balkan nation in July 2024 in more than 100 containers. Thailand rejected the consignment following claims by an environmental group that it was illegal toxic waste. The shipment then returned to Albania.

The law enforcement operation is not finished and "follows the results of analyses from a laboratory in Italy, which confirmed that the materials are toxic waste", the spokeswoman said.

Albanian customs documents indicated the shipment contained iron oxide, a legal export.

But the environmental group Basel Action Network (BAN) cited a whistleblower as saying it contained electric arc furnace dust, a toxic byproduct of steelmaking.

Experts in Albania began taking samples from the shipment last October as part of an investigation into smuggling of prohibited goods.

At the time, prosecutors said they had opened an investigation into suspected smuggling and abuse of office in cooperation with the European Anti-Fraud Office.

They requested several public institutions make their laboratories and experts available for analyses.

The samples were eventually sent to the laboratory in Italy, a prosecution spokeswoman said.

BAN founder Jim Puckett said earlier it was "difficult to understand why the prosecutors' office took so long to have the waste sampled and analysed".

The toxic material could have leaked or been tampered with, he warned.

Environmental NGOs say industrial waste is often shipped by Western countries to be processed in Asia and Africa, in a global trade they estimate may be worth up to $82 billion a year.