Switzerland-based Trafigura today became the second major trading house to confirm that it had traded with an Iranian firm that the European Union says has links to Iran's nuclear programme.
The two contracts demonstrate the difficulties that western powers face in curbing Iran's ability to do business with the rest of the world.
Commodities giant Glencore had supplied thousands of tonnes of alumina to an Iranian firm that provided aluminium to Iran's nuclear programme, Reuters reported last week, citing intelligence and diplomatic sources.
Trafigura, the world's third-biggest trader in raw materials, confirmed it had supplied the Iranian Aluminum Company (Iralco) with alumina in exchange for aluminium, after an industry source said Glencore was not the only major firm sending such shipments.
"We can confirm that Trafigura has traded with Iralco in the past. In October 2011, a physical swap agreement was reached whereby Trafigura provided alumina to Iralco in return for aluminium for Trafigura to export worldwide," the trader said in an emailed statement.
"No deliveries have been made or exports received since new EU sanctions were published in December 2012. The Trafigura Group companies are compliant with national and international law where applicable," it added.
It did not give further details of the barter deal, the value of which is unclear.
Switzerland-based Glencore also said last week that its deal had ended when EU sanctions targeting Iralco came into force. It said its barter contract was legal and denied any wrongdoing by the firm or attempts to help Iran bypass sanctions.
Iran denies allegations by Western powers and their allies that it is seeking atomic weapons and has refused to stop enriching uranium.
As a result, in addition to four rounds of U.N. sanctions, Iran has faced increasingly tougher U.S. and EU measures specifically targeting its financial and energy sectors.
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Iran imports most of its alumina requirements from countries such as China, Russia and Canada and typically buys around 350,000 tonnes a year, according to metals consultancy CRU.
The raw ore is then used in smelters in Iran and converted to aluminium, which can be used to make tubes for uranium enrichment gas centrifuges as well as products such as cans, cars and aircraft.
Barter deals are reasonably common in countries subject to economic sanctions, which make it difficult to send payments through banks.
A spokeswoman at the Swiss Economics Ministry declined to comment on the Trafigura contract, citing commercial secrecy. She said that Iralco was not currently subject to sanctions in Switzerland.
Iralco is not under U.S. or U.N. sanctions, although a legally binding U.N. Security Council Resolution from 2010 urges governments to ban anything that the state determines "could contribute to enrichment-related" activities.
Trafigura, which is currently considering listing subsidiary Puma Energy, is chaired by Claude Dauphin, who was a protege of veteran oil trader Marc Rich.
It has made headlines in the past for its trade with Iraq under the United Nations' oil-for-food programme.
In a settlement, Trafigura agreed to pay a $5 million fine after one of its tankers was intercepted on suspicion of carrying illegal Iraqi crude in 2001. It was not charged with smuggling and denied wrongdoing.