The US government made clear Tuesday when Trump announced the end of US participation in the JCPOA nuclear deal that going ahead, Washington was going to ramp up pressure on the IRGC and the Central Bank of Iran.
On Thursday the United States imposed sanctions against six individuals and three companies.
The action comes two days after President Donald Trump announced that the USA was pulling out of the Iran nuclear deal and reimposing sanctions that were in place before the 2015 agreement.
On Wednesday Supreme Leader, Ayatollah Ali Khamenei, cast doubt on the ability of the European signatories to guarantee Tehran's interests, adding: "I do not trust these countries either".
The IRGC is by far Iran's most powerful security entity and has control over large stakes in Iran's economy and huge influence in its political system. With thousands of troops and advanced military equipment, the Guards have been behind many of Iran's key military operations. Resistance is the only way to confront these enemies, not diplomacy.
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All of the three entities are registered in Iran, according to the statement.
The Treasury Department said one of the companies sanctioned was also involved in retrieving oil revenue from foreign bank accounts held by the Iranian central bank for IRGC-QF activities.
Asked how he would respond if Tehran restarted its nuclear efforts, Trump threatened that "Iran will find out". "If they do, there will be very severe consequences".
The deal, which was reached between Tehran and six world states following a decade of negotiations, put limitations on parts of Iran's nuclear program in exchange for removing all nuclear-related sanctions.
What has Iran been doing?