The implications of the US withdrawal are multi-faceted.
Under the deal signed in Vienna with six world powers - China, France, Russia, the United Kingdom, the US, Germany, and the European Union - Iran scaled back its uranium enrichment programme and promised not to pursue nuclear weapons in exchange for the lifting of economic sanctions.
Trump announced a USA withdrawal from the 2015 nuclear deal on Tuesday and said he was preparing new sanctions against Iran.
Iran has claimed its nuclear program is for civilian purposes and denies supporting extremists in the region.
In a statement published Friday, Iranian Foreign Minister Javad Zarif said he would embark on a round of worldwide diplomacy to try and save the deal. Merkel said it was important to maintain a "strong transatlantic partnership" but added: "If everybody does what they like, then this is bad news for the world". "The inspectors say nothing", she said. If the United States punishes European companies for doing business with Iran, foreign companies will likely walk away from Iran. Zanganeh said foreign investment was needed to develop Iran's its oil industry, but that it could survive even if foreigners made a decision to stay away for fear of USA penalties.
Crude prices slipped on Thursday, giving up early gains as investors took profits on a rally triggered by potential disruption to oil flows from Iran.
Fellow signatories to the deal have been quick to denounce Trump's decision.
In reaction to a Tweet last month by Trump that accused OPEC of "artificially" boosting oil prices, Zanganeh said "Trump is not honest about oil prices".
Planemakers Airbus and Boeing, oil companies and auto manufacturers like France's Renault and Peugeot could be among companies hardest hit.
The statement said "the Iranian regime's reckless actions pose a severe threat to regional peace and security".
These reported remarks come as Iranian Foreign Minister Mohammed Javad Zarif embarked on a diplomatic tour to try and save the nuclear deal.
After seeing the USA flag and a symbolic copy of the JCPOA being set ablaze, Parliament Speaker Ali Larijani dismissed Trump's comments as cheap.