The US said on Thursday that it had imposed sanctions on the Iranian construction sector and trade in four materials used in its military or nuclear programmes.
But it waived sanctions to let foreign companies continue non-proliferation work in Iran.
The decisions announced by the US State Department reflect an effort to increase economic pressure on Iran by putting wider sections of its economy under sanctions.
But they also left open a door to diplomacy by allowing work to proceed at Iranian nuclear plants that make it harder for Tehran to develop a weapon.
US Secretary of State Mike Pompeo had determined Iran's construction sector was controlled directly or indirectly by the Islamic Revolutionary Guard Corps, which Washington has designated a foreign terrorist organisation.
Mr Pompeo also identified four "strategic materials" as being used in connection with nuclear, military, or ballistic missile programmes, placing sanctions on their trade.
"With these determinations, the United States will have additional authorities to prevent Iran from acquiring strategic materials for the IRGC, its construction sector and proliferation programmes," State Department spokeswoman Morgan Ortagus said.
The four materials were types of stainless steel and stainless steel tubes, and manganese brazing foil.