Glencore has traded large quantities of alumina feedstock to Iranian Aluminium Company (Iralco), which supplies aluminium to the Iran’s nuclear programme, Reuters reported, citing intelligence and diplomatic sources.

The Switzerland-based commodities major reportedly traded thousands of tonnes of the mineral last year with Iralco in exchange for a smaller amount of aluminium metal.

Iralco, which has a supply contract with Iran Centrifuge Technology Company (Tesa) was subjected to EU sanctions in December 2012. Glencore announced it has since stopped trading after learning about the Iralco-Tesa relationship.

Barter deals with Iranian companies have become increasingly common as Western sanctions against Iran’s financial and industrial sectors have tightened over the last year.