The US has placed new sanctions on Iran and a top American official has said more measures will follow, further restricting the Islamic Republic’s ability to export oil. Iran is exporting a fraction of the crude it previously shipped because of sanctions and the US may look to tighten the flow of other oil products next.

The US Treasury Department imposed new restrictions on a shipping network controlled by Iran’s Islamic Revolutionary Guard Corps on Wednesday. “There will be more sanctions coming,” Brian Hook, the US special envoy for Iran, said at the State Department soon after the announcement.