With Washington’s economic sanctions against Tehran set to continue even after implementation of the nuclear deal, investment in what many believe is the world’s last great emerging economy may prove too risky for US firms

American companies risk missing out on a “gold rush” in Iran if sanctions are lifted as expected this year under the controversial nuclear deal, experts have warned.

Companies from Asia and Europe are already flocking to do business in the emerging economy, which is set to come in from the cold should Tehran meet its obligations to not pursue a nuclear weapon.

But while the accord has been billed as a flagship of Barack Obama’s foreign diplomacy, the US might be among the last to benefit commercially. Only a small fraction of US sanctions – those related to Iran’s nuclear activities – will be suspended as part of the deal, which also allows for a “snapback” of all sanctions in the event of non-compliance.

Although US companies’ foreign subsidiaries will be allowed to engage with Iran, a minefield of regulatory, transparency and legal issues could present more risk than reward in the eyes of many. Investors are also likely to be wary of the next US presidential election, with Republican candidates vowing to scrap the deal if they come to office.

Other countries, however, appear to have embraced the deal and Iran’s potential as a sleeping giant. “If you want to see optimism, you just go to Dubai airport at about 8am,” Adam Smith, a lawyer focused on international trade compliance, told the Atlantic Council thinktank in Washington recently. “Ten flights a day between Dubai and Tehran, all packed.

“It’s really quite amazing and every discussion you have with big companies, small companies, middle companies throughout the Gulf starts exactly the same way. They say, ‘Mr Smith, please have some tea. Let me tell you about my recent trip to Tehran.’ It’s exactly the same discussion every single time. Even companies that are subsidiaries of US companies: really, it’s everybody.”

Smith struck a cautionary note about the long-isolated economy, however. “But I think to understand what’s going on you have to be comfortable with having some cognitive dissonance, shall we say, over some inconsistencies here. While there’s incredible, palpable excitement at a real gold rush that’s going to happen, or is already happening, depending who you talk to, there’s also real fear. You scratch a little bit below the surface and there’s real fear.

“It’s not so much the companies that have set up in the free zones in Dubai. It’s the necessary ancillary components when it comes to fair dealings with Iran. What do the banks think? What do the insurers think? What do the investors think? This is where the fear actually comes in.”

Speaking at the same event, Nadereh Chamlou of the National Iranian American Council suggested that Americans were being uncharacteristically downbeat and lacking in can-do attitude. “I actually sense a great deal of pessimism in this room,” she said. “Whenever Americans talk, they talk in very pessimistic terms. I think five minutes after you arrive in Iran you will see the incredible potential the country has ... Already what you find in the country is mind-boggling.”

Chamlou has visited Iran three times this year and recently organised a visit by 35 of her former World Bank colleagues, including half a dozen Americans, who found it an eye-opener. She added: “They kept telling me, ‘Take us to where the real Iran is.’ I kept saying, ‘This is the real Iran! Where do you want me to take you?’

“They were asking, ‘Where are all the people dressed in black from top to toe? Where are all the poor people?’ They were amazed. People looked good and well fed. They dressed nicely in the stores. Tehran is a very clean city; you don’t find a cigarette butt anywhere.”

Iranian president Hassan Rouhani, visiting New York earlier this year, sought to persuade American chief executives that Iran’s door is open, and this week the country sent a major shipment of low-enriched uranium materials to Russia, a key step in implementing the nuclear deal. The US is determined to maintain sanctions, however, over issues ranging from Tehran’s sponsorship of terrorism to its poor human rights records to its continued testing of ballistic missiles in defiance of the UN security council.

Chamlou said: “The constraints are more on the American side. I think the world is watching the United States more than it is watching Iran. It is important to really keep a little bit of an optimistic perspective in mind. The other countries are doing it. When you go to Tehran, it’s impossible to find a hotel room. It’s impossible to find a hotel room in any of the other cities as well.”

As the US Congress continues to snipe at the deal, Asian and European countries face significantly lighter restrictions on operating in Iran. British chancellor George Osborne has said he will lead a party of UK businesses to Tehran in 2016. Glenmore Trenear-Harvey, a British intelligence analyst who went on a fact-finding trade mission in October, observed: “We were very much johnny-come-lately. So many delegations were already ahead of us.

“Americans, at the moment, are really going to be at the end of the queue ... As often happens, politicians haven’t the faintest idea of the commercial implications of bloviating.”

With a population of 80 million, Iran has been described as the world’s last great emerging economy. Despite its huge oil and gas reserves, US energy companies are treading carefully. Sara Vakhshouri, president of SVB Energy International, said: “I really cannot imagine in 2016 seeing any major US energy companies going in.

“Very important for these firms is security. Even if the sanctions are lifted, if you’re Chevron or ExxonMobil and you’re sending American personnel to Iran, you’re going to be concerned until relations are normalised.”

But Iran’s youthful population, promising internet sector and middle class consumer base could prove tempting for less capital-intensive enterprises. Jeff Furman, chairman of the board of directors at ice cream maker Ben & Jerry’s, said: “This is total speculation, but the companies that require less investment are the most likely to go in. There’s less risk for Starbucks or McDonald’s to get a foothold with a few stores. It’s an easier thing to do than building a hotel.”

Apple, Hilton Worldwide, McDonald’s and Starbucks declined to comment on any possible plans.

Not everyone regards Iran as a golden egg, however, especially compared with the likes of Cuba, which is geographically and culturally closer to many Americans. Kenneth Katzman, a specialist in Middle East affairs at the Congressional Research Service, told the Atlantic Council: “The problem is the US economy is a $14tn economy. The European economy is a $14tn economy. There are not US companies that are so active in complaining why they’re being shut out and the fact the US trade ban is not being lifted and they’re not participating, with the exception of some of the energy companies.

“It’s not just a big enough deal for them to risk political capital to go against criticism of the deal. Iran is very far away, it is very unfamiliar and there is a very negative perception among many corporate leaders. The memory is of the hostage crisis and all the various schisms, et cetera ... This is just not something that American companies are really going to be up in arms about.”