Western sanctions on Iran contributed to a drop in Iran's access to global sources of capital last year, the US Treasury department said in a report to Congress.

Foreign banks cut their lending exposure to Iran by the equivalent of $9.1 billion in 2012, down 53 per cent, said the report, a copy of which was obtained by Reuters on Thursday.

The report, which cited information from the Bank of International Settlements, said broader international sanctions against Iran and other perceived weaknesses in the investment climate in Iran also contributed to the drop.

The US and the EU have imposed sanctions on Iran that aim to slow funding to Tehran's nuclear program. The West says the program is developing nuclear weapons, a charge Tehran denies.-Reuters