Hong Kong's flagship carrier Cathay Pacific has suspended flights over Iran and the Caspian Sea after the European Aviation Safety Agency issued a warning about missiles being fired at Syria.
The EASA stepped in as Russia intensifies its air campaign against Islamic militants in Syria. Last week, Moscow launched a salvo of cruise missiles from its warships in the Caspian.
Cathay said on Wednesday (local time) it had suspended flights in response to the dangers.
"In view of the situation in the region, Cathay Pacific suspended all flights over Iran and Caspian Sea since last Thursday until further notice," it said in a statement.
The airline said it had received safety advisories from both the EASA and the United Nations' International Civil Aviation Organisation, but added that neither had made specific recommendations to carriers.
Cathay already has a long-term policy not to overfly Iraq, Afghanistan, Ukraine and Syria, the statement said.
In its safety bulletin released last week, EASA said "missiles en-route to Syria crossed airspace in Iran and Iraq below flight routes used by commercial transport aeroplanes".
The missiles had been launched from the Caspian Sea, it said, adding that the advisory was to "create awareness" for airspace users.
Australian carrier Qantas said on Wednesday it had chosen not to suspend flights over the area.
"The Europeans said that those issues were there, but didn't make any recommendations or changes to what airlines do," said chief executive Alan Joyce.
"If there was a problem, and if does turn into being a problem, Qantas will not be flying aircraft through that airspace. But the information that we have is it is safe to do so."
Qantas flies over Iran on its Dubai to London leg.
Singapore Airlines said in a statement on Wednesday that it had "resumed normal routings" after previously diverting some flights to avoid the Caspian Sea area.
It did not explain why it had resumed those services.
The airline said decisions on flight routes were made "based on numerous factors" and added that it only used routes that had been cleared for use by the authorities.
"The safety of our customers and crew is our number one priority," the statement added.
Russia said on Tuesday its air force had hit 86 "terrorist" targets in Syria in the past 24 hours, the highest one-day tally since it launched its bombing campaign on September 30.
The air safety fears come as investigators on Tuesday issued their final report into the fate of Malaysia Airlines Flight 17, concluding it was shot down by a Russian-made BUK missile fired from war-torn eastern Ukraine.
The Boeing 777 was downed last year, killing all 298 people on board.
Dutch Safety Board chairman Tjibbe Joustra criticised Ukraine and other authorities for a failure to recognise the risk of flying above a war zone.
The report said that between July 14 and 17, a total of 61 airlines from 32 countries used the airspace above eastern Ukraine and on July 17, the day of the crash, 160 flights were guided through.
It also said that between the end of April and July 17, at least 16 Ukrainian armed forces' helicopters and planes, including fighter aircraft, had been shot down in the war zone.