A new Swiss payment mechanism has launched which allows humanitarian aid to be sent to Iran without falling foul of US sanctions.
Cancer and transplant patients are the first to have benefited.
The US said the channel was subject to "strict due diligence measures to avoid misuse by the Iranian regime".
Humanitarian supplies are exempt from the US sanctions, but the measures have deterred several foreign banks from doing any business with Tehran.
The Swiss government said the new payment mechanism was aimed at ensuring that companies based in Switzerland had a "secure payment channel with a Swiss bank through which payments for their exports to Iran are guaranteed."
"In this way, Switzerland is helping to supply the Iranian population with agricultural commodities, food, medicines and medical equipment. This is in keeping with Switzerland's humanitarian tradition," it said.
Under the rules of the new mechanism, the US provides assurances that transactions are not violating sanctions, the Swiss government statement added.
In turn, exporters and participating banks provide information on their business activities and partners in Iran.
As a pilot transaction, a payment was made for a shipment of cancer drugs and drugs required for organ transplants worth some €2.3m ($2.55m; £1.9m).
The US Treasury Department confirmed the completion of initial financial transactions through the new payment mechanism, saying they provided a "model for facilitating further humanitarian exports to Iran".
Treasury Secretary Steven Mnuchin said the US government had full confidence that the mechanism "will improve the flow of humanitarian goods to the Iranian people."
"Humanitarian transactions are currently allowed under our sanctions programs, and we encourage companies to use this humanitarian mechanism," he added.
The US reinstated economic sanctions on Iran after President Donald Trump abandoned a landmark deal in May 2018 aimed at curbing Iran's nuclear ambitions.
Mr Trump has said he wants to apply "maximum pressure" on the government in Tehran to compel it to renegotiate the accord.
The launch of the new payment channel comes after a peak US-Iran tension.
In January, a top Iranian military commander, General Qasem Soleimani, was killed in Iraq in a US drone strike.
Days later, Iran shot down a Ukrainian passenger jet with 176 on board - the military said it was mistaken for a US cruise missile.
Those killed included dozens of Iranians and Canadians, as well as nationals from Ukraine, the UK, Afghanistan and Germany.