Moderate cleric Hassan Rouhani was to be inaugurated for a second term as Iranian president in front of foreign guests on Saturday.
In a meeting with Mogherini prior to the ceremony, Foreign Minister Mohammad Javad Zarif said the European Union needs to be "alert" to Trump's efforts "to undermine the deal laying the blame on Iran".
The ministerial line-up is due to be officially unveiled on Saturday, but reformist allies are angry over news that Rouhani will unveil another all-male cabinet. Trump said in a statement on the occasion of signing of the law the document was flawed and some of its provisions stood at variance with the US Constitution.
Iranian officials say they have prepared a 16-point document for how they will respond to the new sanctions, without giving details.
Khamenei, for his part, was quoted as saying that, "Despite ongoing attempts to isolate Iran, the nation has not been isolated and continues to cooperate with the world while also challenging the hegemonic powers". The Trump administration and Congress have been busy slapping a variety of sanctions, some unprecedented, on Iran for its conglomerate of belligerence. An arms embargo will be enforced and Iran's prestigious Revolutionary Guard will face terrorism sanctions.
Rouhani, 69, was decisively re-elected in May with around 57% of the vote.
However, his inauguration came less than 24 hours after fresh sanctions were imposed by US President Donald Trump, who has threatened to tear up the nuclear deal entirely.
Iran has been complaining that the United States, as another party to the deal, has been seeking to sabotage worldwide - including European - trade with Iran.
But the Europeans do oppose Iran's recent missile tests, with the French foreign ministry stating on Thursday that they "contradict" UN Resolution 2231 which oversees the nuclear deal, and "constitute a potential threat to stability and security in the region". "We prefer peace to war and reform to rigidness", said Rouhani.
Rouhani also called America "a country that isn't reliable when it comes to global issues".