The US terrorism label for Iran's Revolutionary Guard Corps (IRGC) took effect on Monday, according to a notice published in the US Federal Register.
US President Donald Trump said last week he would make the unprecedented move, which was immediately condemned by Iran, and created concerns about reprisal attacks on US forces.
The IRGC is in charge of Iran's ballistic missile and nuclear programs. It also is involved with the country's banking and shipping industries. The new designation makes it easier to prosecute companies or people in the European Union that do business with Iran, Reuters reported.
US law already punishes US persons who deal with the IRGC with up to 20 years in prison because of the group's designation under the US Specially Designated Global Terrorist list, a different US sanctions program, the news agency said.
Also Monday, Iranian Foreign Minister Javad Zarif issued a "reminder" to European powers that Tehran is allowed to enrich uranium under its nuclear deal, after a senior French diplomat claimed otherwise.
"There is no prohibition on the enrichment of uranium by Iran," Zarif tweeted.
His comments were addressed to France, Germany and Britain who signed up to the landmark 2015 accord with Tehran under which uranium enrichment is curtailed but not banned.
Zarif's remark follows France's ambassador to Washington declaring: "It's false to say that at the expiration of the JCPOA (nuclear deal), Iran will be allowed to enriching uranium."
The claim on Saturday by Gerard Araud has since been deleted from his Twitter account, Agence France Presse reported.
Under the 2015 agreement, Iran can only enrich uranium to 3.67 percent -- far below the roughly 90-percent level needed for nuclear weapons, it said.
