The profits from the companies fund Iran's missile programme, the US says
The US Treasury has imposed sanctions against companies connected with the Iranian Islamic Revolutionary Guards.
The action extends earlier sanctions against the Guards and its construction company headquarters.
It aims to freeze the foreign assets of four companies connected to Khatam al-Anbiya Construction and its chief officer.
The company's profits help fund Iran's nuclear and missile programmes, the US Treasury said.
Washington says the company is the construction arm of the Iranian Revolutionary Guards, which is a wing of the Iranian army, founded after the 1977 revolution.
The US Treasury named the company's head as Revolutionary Guard General Rostam Qasemi, who has also had assets outside Iran frozen under the sanctions.
Khatam al-Anbiya builds infrastructure like highways and tunnels, with profits going back into the Iranian military programme to develop what the US Treasury called "illicit activities".
These included "WMD proliferation and support of terrorism", according to a statement released on the US Treasury website.
The treasury statement said the Guards were consolidating control over broad swathes of the Iranian economy, displacing ordinary Iranian businessmen in favour of a select group of insiders, and hiding behind groups like Khatam al-Anbiya to maintain ties to the outside world.
The treasury announcement is yet another signal of how individual countries are planning to tighten the noose on Iran's authorities, even while pushing for further UN sanctions.
US President Barack Obama said on Tuesday the US and its allies were moving "fairly quickly" towards adding new sanctions on Iran, in an attempt to curb its nuclear programme.
Earlier on Wednesday, Russian Deputy Foreign Minister Sergei Ryabkov said the US and its European allies were pushing Russia towards agreeing to further sanctions on Iran.
For now, the US under President Obama is leading by continuing efforts started under previous administrations.
Germany, meanwhile, has suggested it could consider targeting Iran with economic sanctions, and even Russia has made some noises to that effect.
Tehran insists its nuclear programme is strictly peaceful in nature.
But it has said it will continue to enrich uranium to 20%, higher than it has ever done before.
A nuclear weapon requires uranium to be enriched to 90%, experts say.
The jump from the low levels of enrichment currently available to Iran to 20% is the most difficult step toward enriching nuclear material to weapons grade, the experts add.