As a US citizen or permanent resident (green card holder) you are required to report income and pay taxes on any income you have anywhere in the world. Holding assets is not by itself income, and there are no taxes on transferring assets (such as cash or securities) from a foreign bank account to a US bank account.
However, assets may generate income. For example, if you have a bank account that pays interest or dividends, that income is taxable, and it doesn't matter if the income is paid in foreign currency in an overseas account, or if that income is paid in a US bank account.
Selling your home in Iran may generate income if you sell it for more than you paid for it (plus the cost of any permanent improvements you may have made.) This is a capital gains -- when you sell property that you have held more than one year you have a capital gain if you sell for more than you paid for the asset, and the capital gains income is generally taxed at a lower rate than ordinary income.
From the IRS point of view, they only want their taxes paid on income, so the IRS won't particularly care if you move cash accounts from one country to another (although they may be notified, it's not taxable to transfer assets you own from one place to another.) For other legal questions on the sanctions you may need to contact the State Department.
