A total of 102 containers, believed to be filled with suspicious waste, were unloaded in the port of Durres from a Turkish-flagged container ship in November and taken to a "secure location", the authorities said.

At the time, the Durres prosecutor's office said it had launched an investigation into "smuggling of prohibited goods" and "abuse of power", in cooperation with the European Anti-Fraud Office OLAF.

The containers left Albania last July, and according to customs documents at that time, its cargo consisted of industrial waste, specifically "iron oxide", whose export is authorised.

But information passed on by a whistleblower to the Basel Action Network (BAN) suggested the cargo actually contained "hazardous waste pollution dust from secondary steel mills", according to a statement by BAN and environmental NGO Milieukontakt Albania obtained by AFP.

The two groups denounced the "complete silence from the government and the apparent lack of any progress on the case from the government of Albania and the Durres prosecutor's office".

It was planned that the contents of the containers be sampled and analysed by independent laboratories, the statement said.

But the groups said: "We are not even sure that the samples have been taken and the analysis begun."

Illegal trafficking in hazardous waste is a serious matter requiring criminal sanctions, the organisations added, urging the authorities to provide updates.

Contacted by AFP, the Durres prosecutor's office said their "investigations are continuing as a matter of priority", without elaborating.

Thailand rejected the cargo and it returned to Albania after several months at sea, with stopovers and ship changes in various countries including Spain, Portugal, Italy and Turkey.

According to environmentalists, so far all indications point the waste comes from the Kurum steel mills in Elbasan, central Albania.

The shipment of industrial waste from Western countries to be processed elsewhere in the developing world is a global business estimated to be worth between 44 billion and 70 billion euros ($46 billion to $74 billion) annually, according to environmental NGOs.