WASHINGTON, Nov. 6 (Xinhua) -- The United States is beefing up its sanctions against Iran's banks by banning certain types of fund transfers, the Treasury Department said Thursday.

    Previously, U.S. financial institutions were authorized to deal with certain money transfers for Iranian banks and other Iranian customers as long as the payments were initiated offshore by a bank that was not neither Iranian nor American and only passed through the U.S. financial system en route to another offshore bank that was neither Iranian nor American.

    "As a result of today's action, U.S. financial institutions are no longer allowed to process these U-turn transfers," the department said. "This regulatory action will close the last general entry point for Iran to the U.S. financial system."

    The United States and its Western allies have long accused Iran of developing nuclear weapons and supporting insurgents in Iraq. U.S. sanctions against Iran have been going on for decades. Iran always denies U.S. charges.