China has overtaken the European Union to become Iran's largest trading partner, according to analysis of the commercial ties between the two countries.
The growing business links between Beijing and Tehran underline China's reluctance to agree to any further economic sanctions on Iran as western countries escalate their campaign to contain the country's nuclear ambitions.
The announcement by Mahmoud Ahmadi-Nejad, the Iranian president, that Iran will start enriching uranium to 20 per cent purity – a step closer to the 90 per cent required to build nuclear weapons – has given renewed impetus to western calls for the United Nations Security Council to impose more sanctions.