US Treasury Secretary Steve Mnuchin has said he expects President Donald Trump to impose new sanctions on Iran.
The news comes as Mr Trump faces a Friday deadline to decide whether to waive other major sanctions on Iran lifted under the 2015 nuclear deal.
Earlier, European powers urged Mr Trump to uphold that agreement, saying it was vital for international security.
Mr Trump has criticised the deal, which saw sanctions lifted when Iran agreed to limit its nuclear fuel production.
Mr Mnuchin told reporters he was expecting new sanctions on Iran to be announced - which previous reports have suggested could be targeted measures against Iranian individuals and businesses.
The US president says he wants to amend the deal - or withdraw from it completely.
The foreign ministers of Britain, France, Germany and the European Union met their Iranian counterpart Mohammad Javad Zarif in Brussels on Thursday to reaffirm their commitment to the accord, which was also backed by China and Russia.
At a news conference afterwards, representatives of the EU, the UK, France and Germany reiterated their support for the nuclear deal they helped negotiate.
UK Foreign Secretary Boris Johnson insisted the deal was preventing Iran from acquiring nuclear weapons, and challenged Washington to come up with a better alternative.
Mr Trump said they included the deal's "sunset clauses", one of which allows for the lifting of restrictions on Iran's uranium enrichment programme after 2025.
He also wants to give the International Atomic Energy Agency access to Iranian military sites, and for the deal to cover Iran's ballistic missile programme.
The US and EU say Iranian ballistic missile tests conducted in the past year have violated UN Security Council resolution 2231, which endorsed the nuclear deal.
The resolution calls upon Iran not to "undertake any activity related to ballistic missiles designed to be capable of delivering nuclear weapons, including launches using such ballistic missile technology".
Iran says the missiles it has tested are not designed to carry nuclear warheads and insists its nuclear programme is entirely peaceful, reports BBC.