WASHINGTON—The U.S. took a step toward cutting Iran off from the global economy on Thursday, levying sanctions on a financing network and accusing the country’s central bank of helping funnel U.S. dollars to the blacklisted elite military unit known as the Quds Force.

Acting jointly with the United Arab Emirates, the U.S. Treasury Department imposed sanctions on several Iranian companies, individuals and officials it said are operating an illegal currency-exchange network in the U.A.E.

The sanctions were the first since President Donald Trump this week pulled out of the landmark Iran nuclear deal and announced a return to economy-crippling sanctions against Tehran, and represented a move toward cutting off the Middle East country’s access to dollars.

The actions Thursday foreshadow the return of greater U.S. economic penalties as Washington reimposes sanctions that were lifted as part of the 2015 nuclear agreement. Iran’s central bank wasn’t formally sanctioned in Thursday’s actions, but will be in the coming months, under Mr. Trump’s plan to reimpose U.S. penalties.

The Trump administration is leveraging the U.S.’s economic heft and the dollar as the world’s reserve currency to pressure Iran, European countries and other nations into reaching a new nuclear agreement. The administration wants a deal that not only permanently restricts Iran’s nuclear program but also stymies its ballistic-missile efforts and curbs Tehran’s support for militants fighting across the region.