The USA has announced further action against Iran by imposing sanctions on its iron, steel, aluminium and copper sectors.
Iran, hard hit by US sanctions on its oil sales, face the new restrictions on metal exports, but experts have advised that these may be harder to sanction.
President Donald Trump last week imposed sanctions aimed at punishing anyone who buys or trades in Iranian iron, steel, aluminum or copper.
That came after Washington in November re-instated sanctions aimed at slashing the Islamic republic's oil exports, by far its top source of foreign currency.
But the steel and mining sector, Iran's second-largest source of foreign revenue, may prove harder to target.
Relatively decentralised, made up of small and medium-sized companies and selling mostly to nearby countries, it is less vulnerable to sanctions, experts say.
"The US cannot completely stop exports. Some countries, companies with no US ties, are OK to work with Iran," said industry analyst Mojtaba Fereydouni.
"Also our main export markets are our neighbours -- Iraq and Afghanistan, and recently Syria and Oman."
He pointed out that Iranian metals firms, no strangers to sanctions, were relatively unscathed by an initial tranche of restrictions re-imposed last year.
"In August, steelmakers were barred from importing essential raw materials and any trade in steel products… yet exports are up" for the year, he said.
According to official data, Iran's mineral exports grew about 20 percent year-on-year to $6.2 billion in the 12 months to March, with steel making up over two-thirds of that figure.