An Iranian man walks past the stock exchange building in the capital Tehran. BEHROUZ MEHRI | AFP | Getty Images

Iran's fragile economic recovery is in jeopardy with President Donald Trump widely expected to scrap an internationally-brokered nuclear deal and re-impose sanctions against the regime. Trump has given the European nations that helped broker the 2015 nuclear deal — which he called "terrible" — until May 12 to change it, but that is looking increasingly unlikely. Iran has said it won't accept changes to the deal, which saw it reigning in its nuclear ambitions in return for a relaxation of international sanctions that had sorely damaged the oil exporter. Europe has so far failed to convince Trump to save the nuclear agreement, known formally as the Joint Comprehensive Plan of Action (JCPOA). Where sanctions will hurt most? Now, those sanctions are likely to return and Iran's economy, which was slowly recovering due to the nuclear deal, could suffer again — particularly in key sectors for the economy, such as oil and banking. "We are expecting that Trump will withdraw from the nuclear deal on May 12 and this is likely to come with a first step of re-imposing sanctions related to Iran's oil sector," Dalia Naguib, MENA Analyst at advisory services firm Frontier Strategy Group, told CNBC Tuesday. "We could see more sanctions come back related to strategic sectors like the auto sector or around Iran's shipping sector," she told CNBC's Squawk Box Europe.

Iran's oil is the main source of its export earnings but agriculture, the services sector, manufacturing and financial services are also pillars of the economy too, according to the World Bank. The bank noted in a report last year that Iran's growth prospects relied on the pace of Iran's reintegration with the global economy in terms of banking, trade and investment. But if further sanctions are imposed on Iran, companies and international banks are unlikely to touch the country during that time, one analyst said. "As always, the parts of the economy that will be worst hit are the parts that are most internationally-connected," Marcus Chevenix, MENA analyst at independent research firm TS Lombard, told CNBC Tuesday. "And those parts in Iran are oil and banking. If I had to flag up an area that was very vulnerable it would be banking," he said. Chevenix said that if the U.S. decided to impose "secondary sanctions" on Iran, it could prevent European firms doing business with the country, even if they wanted to. Secondary sanctions deter other countries or institutions (such as European banks) from doing business with Iran because they don't want to be blacklisted — or "exposed" as Chevenix said — by the U.S. for doing so, effectively cutting off Iranian business from access to external investment and financial systems. "If Trump was to impose secondary sanctions, he could cut off the Iranian banking system from the rest of the world and that would take us back to a pre-2015 situation. The U.S. has all sorts of unilateral power here," he said.

Sanctions 'very bad' for Iran