The US State Department announced that it has sanctioned a section of Iran’s construction sector that is directly or indirectly tied to the Islamic Revolutionary Guard Corps (IRGC). The US had previously designated the IRGC as a terrorist organization in order to increase pressure on Iran with more economic sanctions while leaving a door open to diplomacy by allowing work to proceed at Iranian nuclear facilities, which makes it harder for Iran to develop a nuclear bomb.

The State Department spokeswoman Morgan Ortagus announced on Friday that the United States is determined to prevent Iran’s access to the four strategic materials that are used in ballistic missile, nuclear, and military programs, on top of sanctioning IRGC’s construction sector “to prevent Iran from acquiring strategic materials for the IRGC, its construction sector, and its proliferation programs.”

According to Reuters, the United States plans on allowing Russian, Chinese, and European companies to continue their work in Iranian nuclear facilities in order to make it harder for Iran to develop a nuclear weapon.

The Trump administration would let the work go forward by issuing waivers to sanctions that bar non-American companies from dealing with the Atomic Energy Organization of Iran (AEOI).

According to sources familiar with the matter, the waivers have been renewed for 90 days.