Iran closed its airspace for nearly five hours amid concerns about a possible military clash between the US and Tehran.
Airlines were forced to cancel, reroute or delay some flights after the airspace was closed to all flights except international ones to and from Iran with official permission from 10.15pm GMT on Wednesday.
The notice was removed shortly before 3am GMT, according to tracking service Flightradar24, which showed five flights from Iranian carriers Mahan Air, Yazd Airways and AVA Airlines were among the first to resume over the country.
The temporary closure came as President Donald Trump had been weighing a response to the turmoil in Iran, which is seeing its biggest anti-government protests in years.
The United States was withdrawing some personnel from bases in the Middle East, a US official said on Wednesday, after a senior Iranian official said Tehran had warned neighbours it would hit American bases if Washington strikes.
Meanwhile the British government announced its embassy has been temporarily closed and will operate remotely.
It comes after Sir Keir Starmer earlier said Britain was working with allies on further sanctions against the regime.
Thousands of of anti-government demonstrators have reportedly been killed in the country in recent weeks.
A UK Government spokesperson said on Wednesday: “We have temporarily closed the British Embassy in Tehran, this will now operate remotely.
“Foreign Office travel advice has now been updated to reflect this consular change.”
After threatening intervention, US President Donald Trump softened his tone on Wednesday night as he said killings in Iran’s crackdown on protests were easing and he believed there was no current plan for executions of protesters.
Iranian state media on Thursday reported that 26-year-old Erfan Soltani, who was arrested during protests in the city of Karaj, would not be given the death sentence.
A rights group reported earlier this week that he was due to be executed on Wednesday.
Trump's comments came after fears grew in the Middle East that Washington could launch strikes, following his repeated threats to intervene on behalf of Iranian protesters.
Trump did not rule out possible US military action, however.
The clerical establishment has cracked down hard on one of the biggest challenges to its rule since the 1979 Islamic Revolution. More than 2,500 people have been reported killed in the unrest that spiralled out of protests over soaring prices.
