The US has eased sanctions on exports of medical equipment to Iran, the treasury department has said.
Electrocardiography and dialysis machines are among the items that can now be exported without prior approval.
The department said the expansion of allowed exports was intended to enable "legitimate humanitarian trade".
Iranians have suffered chronic medicine shortages amid Western sanctions aimed at pressuring Tehran to abandon its nuclear programme.
Israel and some Western powers suspect Iran's nuclear programme may be a front for making weapons, but Tehran insists it is purely peaceful.
David Cohen, the US treasury department's under-secretary for terrorism and financial intelligence, said on Thursday the policy shift "reflects an important element of our sanctions policy".
Iranian economic hardship
"Even as we continue to implement and enforce our rigorous sanctions regime against Iran, we are committed to safeguarding legitimate humanitarian trade," he said.
The US has imposed as many as nine sets of sanctions aimed at isolating the Iranian oil and gas, financial and automotive industries from international money and markets.
The international sanctions have contributed to economic hardship in Iran, which is suffering from rising unemployment, a devalued currency and soaring inflation.
Analysts say exceptions for food, agricultural commodities, medicine and medical equipment in the sanctions programmes have not been effective, with many banks still worried they could be penalised for processing such export transactions.
The US has said that even as it imposes sanctions, it remains open to a diplomatic solution with Iran.
Last month, US President Barack Obama said the US had "cautious optimism" it would be able to work with newly elected Iranian President Hassan Rouhani.
"We may be able to move forward on a dialogue that allows us to resolve the problems with Iran's nuclear programme," Mr Obama said.