The Treasury Department accused the men of secretly funneling millions of dollars through an Iraqi bank to help Hezbollah, the militant network that the USA considers a terrorist group.
Also sanctioned Monday are an Iraqi bank, its chairman, and Ali Tarzali, who Treasury said is "the assistant director of the International Department at the Central Bank of Iran".
"Iran's Islamic Revolutionary Guard Corps bears full responsibility for the consequences of its reckless actions, and we call on the IRGC and its militant proxies, including Hezbollah, to take no further provocative steps".
The head of the U.S. Treasury Steven Mnuchin accused Seif in providing financial assistance to Hezbollah, the United States recognized terrorist organization.
The new sanctions are part of the administration's efforts to address Tehran's "malign influence" in the region, an effort that, in conjunction with President Donald Trump's decision to remove the United States from the Iran nuclear deal and Monday's controversial opening of the USA embassy in Jerusalem, has led to a spike in tensions across the Middle East.
That will begin August 7 followed by more robust sanctions on individuals who "knowingly" engage in certain "significant transactions" with the central bank starting November 5.
The sanctions on Seif and Tarzali do not extend to the Bank of Iran; however, President Trump's decision to leave the JCPOA and reimpose sanctions will extend to some of the central bank's transactions. Habib and the bank are also subject to secondary sanctions.
Earlier this month, Iranian President Hassan Rouhani said in a live broadcast that if President Trump follows through with his promise to pull out of the Iran nuclear deal, the United States "will surely regret it".
The U.S. sanctions came as Iranian Foreign Minister Mohammad Javad Zarif was meeting in Brussels with the top French, British and German diplomats as the Europeans seek to keep Iran from bailing on the nuclear deal.
Iran has promised to ramp up its nuclear program if the deal collapses, though many feel as though the deal has done little to diminish Iran's nuclear efforts anyway. These are part of a Trump administration Treasury campaign against the IRGC.
On Thursday, the Treasury announced sanctions against a "large-scale" currency exchange network serving the Revolutionary Guards, hitting six individuals and three companies at the centre of the network. That means that anyone, in any country, who does business with Seif or Tarzali could themselves be punished with sanctions, cutting them off from the U.S. financial system. Most recently, the US has been concerned about the role that Hezbollah fighters are playing in Syria to help prop up President Bashar Assad. And in 2015, the USA targeted the governor of Syria's central bank.