A spokesperson said this on behalf of Foreign Minister Mike Pompeo.
The Americans argue that the construction sector is under the direct or indirect control of the Iranian Revolutionary Guard, the elite unit of the Iranian army that the US regards as a terrorist organization. With the new sanctions, the US wants to prevent Iran from developing a nuclear weapon.
Relations between the two states have been sharper since President Donald Trump withdrew from the nuclear deal with Iran last year and began imposing more and more sanctions.