"We do mean to close down the Central Bank of Iran (CBI)," the official told reporters on condition of anonymity, while adding that the United States is moving quickly to implement the sanctions, signed into law last month.

The sanctions, broadly aimed at forcing Tehran to shift course on its nuclear program, targeted Iran's crucial oil sector and required foreign firms to make a choice between doing business with Iran or the United States.

Foreign central banks that deal with the Iranian central bank on oil transactions could also face similar restrictions under the new law, which has sparked fears of damage to US ties with nations like Russia and China.

"If a correspondent bank of a US bank wants to do business with us and they're doing business with CBI or other designated Iranian banks... then they're going to get in trouble with us," the US official said.

The measures were contained in a mammoth $662 billion defense bill, which President Barak Obama signed on December 31 at a time of rising tension with Tehran, which has threatened to block the Strait of Hormuz -- through which more than a third of the world's tanker-borne oil passes.

The United States has warned it will "not tolerate" such an interruption.

There are fears that increased sanctions on Iran's central bank could force the global price of oil to suddenly soar, and actually give Tehran a financial windfall on its existing oil sales.

Rising oil prices could also crimp the fragile economic recovery in the United States and inflict pain on American voters in gas stations -- at a time when Obama is running for reelection next year.

Copyright AFP (Agence France-Presse), 2012