Considering the banking ban is effectively still in place, it is not possible to use a credit card outside Iran to pay for something inside Iran. So, a conventional booking would not be possible, though a reservation would be, in theory.
Edit with some clarification: The banking ban was American and penalised (pretty much) any company doing business with Iran as well as the US. So, anyone selling airline tickets and doing business with Iran could therefore not do business with, or in, the US. As the American market is somewhat larger than the Iranian market, the choice is easily made.
Note that this ban, in this form, is no longer in place. But, as I pointed out at the top, international bank transfers and payments to and from Iran, are currently not yet available.