The US Treasury has granted plane manufacturer Boeing a licence to export certain spare commercial parts to Iran, a company spokesman says.
Boeing has had no public dealings with Tehran since 1979.
In a statement, the US company said the licence had been granted for the safety of flight.
The step is being seen as part of a temporary agreement to ease sanctions on Tehran that US Secretary of State John Kerry reached with Iran last year.
Under the deal brokered in November, Iran agreed to curtail its nuclear activities for six months in exchange for sanctions relief from nations including Britain, China and the US.
US company General Electric said late on Friday it had received US permission to overhaul 18 engines sold to Iran in the late 1970s. That work would be carried out at GE facilities or at German firm MTU Aero Engines, it said.
Iran Air is still flying passenger planes bought before the 1979 hostage crisis, during which 52 Americans were held hostage in Tehran for 444 days.
Iran has reportedly argued that sanctions imposed after the hostage ordeal have prevented Tehran from upgrading its plane fleet and reduced the safety of its aircraft.
There have been more than 200 accidents involving Iranian planes in the past 25 years, leading to more than 2,000 deaths, reports say.
Boeing has said the licence covers only components required to ensure safe flight operations of planes it sold before Iran's revolution in 1979.
No discussions are to be allowed over the sale of new aircraft when and if sanctions are completely lifted, correspondents say. If a permanent deal is agreed, it is thought likely that Iran would require the purchase of hundreds of new aircraft.