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.
Iran’s Supreme Leader has warned his country will not step back “one iota” from its nuclear rights, as it resumes talks with world powers in Geneva.
Ayatollah Ali Khamenei said he would not intervene directly in the negotiations, but that he had set “red lines” for Iran’s representatives.
President Barack Obama meanwhile urged US senators not to impose new sanctions on Iran to allow time for diplomacy.
He was unsure if it would be possible to reach an interim agreement soon.
“We don’t know if we’ll be able to close a deal with Iran this week or next week,” he told a Wall Street Journal (WSJ) forum in Washington on Tuesday.
President Obama: ”We should be able to achieve a resolution” over Iran’s nuclear programme
US President Barack Obama has said recent moves by Iran should offer the basis for a “meaningful agreement” on its nuclear programme.
Speaking at the UN General Assembly’s annual meeting, Mr Obama said words now had to be matched by actions.
The US leader recently exchanged letters with his newly-elected counterpart over the nuclear issue.
Later, President Hassan Rouhani insisted Iran posed “absolutely no threat to the world or region”.
The office of French President Francois Hollande says he will meet his Iranian counterpart on the sidelines of the UN General Assembly in New York next week.
It comes as President Hassan Rouhani has indicated a more moderate and Western-friendly attitude than his predecessor, Mahmoud Ahmadinejad.
There has been speculation that Mr Rouhani might also meet US President Barack Obama in New York.
Correspondents say this would herald a major thaw in US-Iran relations.
French officials said the meeting between Mr Hollande and Mr Rouhani on Tuesday had been organised at the request of Iran.
Iran’s supreme leader has dismissed a US offer of one-to-one talks on Tehran’s nuclear programme.
Ayatollah Ali Khamenei said in a speech posted online that the US was proposing talks while “pointing a gun at Iran”.
On Saturday, US Vice-President Joe Biden suggested direct talks, separate to the wider international discussions due to take place later this month.
But the US widened sanctions on Iran on Wednesday, aiming to tighten a squeeze on Tehran’s ability to spend oil cash.
Iran, which is subject to an array of international sanctions, has long argued that its nuclear programme is for energy generation and research.
Tehran’s critics believe the government is developing nuclear weapons.
The five permanent members of the UN Security Council plus Germany have held a series of negotiations with Iran over the years.
But they have often ended with Iran demanding the West lifts sanctions as a condition to any nuclear move, and the Western powers refusing.