© Reuters. FILE PHOTO: A vehicle of the airport rescue and firefighting services stands in front as a Boeing 767 aircraft of United Airlines takes off from Zurich airport

By Jamie Freed and David Shepardson

(Reuters) - Some global airlines are re-routing flights to avoid Iran-controlled airspace over the Strait of Hormuz and Gulf of Oman, they said on Friday, after the U.S. aviation regulator barred its carriers from the area until further notice.

Thursday's emergency order from the U.S. Federal Aviation Administration (FAA) came after Iran shot down a high-altitude U.S. drone with a surface-to-air missile, sparking concerns about a threat to the safety of commercial airlines.

The downing of the unarmed Global Hawk drone, which can fly up to 60,000 ft (18,300 m), was the latest in a series of incidents in the Gulf region, a critical artery for global oil supplies, that included explosive strikes on six oil tankers.

According to flight tracking applications, the FAA said, the nearest civil aircraft was operating within about 45 nautical miles of the unmanned aircraft when it was shot down.

"There were numerous civil aviation aircraft operating in the area at the time of the intercept," the FFA said, adding that its prohibition would stay in place until further notice.

Hours earlier, United Airlines suspended flights between New Jersey's Newark airport and India's financial capital of Mumbai following a safety review.

Cathay Pacific, Malaysia Airlines, Australia's Qantas Airways Ltd, Singapore Airlines Ltd, Germany's Lufthansa, British Airways and KLM of the Netherlands said they were re-routing flights to avoid the area.

Emirates Airline and Etihad Airways, which were flying over the area earlier on Friday, according to flight tracking website FlightRadar24, said later they were also re-routing their flights.

'THREAT IS REAL'

The FAA said it remained concerned about the escalation of tension and military activity in close proximity to high-volume civil aircraft routes as well as Iran's willingness to use long-range missiles in international airspace with little or no warning.

In July 2014, Malaysia Airlines Flight MH17 was shot down by a missile over Ukraine, killing all 298 on board, prompting carriers to take more steps to uncover threats to their planes.

But concerns persist over inadequate government intelligence sharing and a reluctance by countries involved in conflicts to divulge information or sacrifice overflight fees by closing their skies, according to safety experts.

The U.S. ban does not apply to airlines from other countries, but OPSGROUP, which provides guidance to operators, said carriers globally would take it into consideration.

"Since MH17, all countries rely on advice from the U.S., the U.K., France and Germany to highlight airspace risk," it said.

"The threat of a civil aircraft shootdown in southern Iran is real," it added.

Restricting airspace complicates airline efforts to keep routes running in a region where airspace is already congested, in part due to ongoing conflicts which have made it unsafe to fly over some countries.

At 0820 GMT on Friday, Flightradar24 showed Qatar Airways flights in the area barred to U.S. carriers.

On Monday, before the drone was shot down, Qatar Airways Chief Executive Akbar al-Baker told Reuters the airline "has a very robust plan B for any eventualities, including if there is a conflict in our region."

Qatar Airways did not respond immediately to a request for comment on Friday on whether it had introduced new measures since the drone was shot down.

Etihad, which had said it was monitoring the situation, later said in a statement it had agreed "to change a number of the flight paths we operate to and from the Arabian Gulf" after close consultation with the UAE General Civil Aviation Authority.

FLIGHTS SUSPENDED

United said it had suspended its flights to India through Iran airspace after a "thorough safety and security review," but did not say how long the suspension would last.

A United spokesman said customers flying from Mumbai to Newark would be booked on alternative flights back to the United States.

"We continue to explore all our options and remain in close contact with relevant government authorities," he added.

A Lufthansa spokesman said the company's planes had been avoiding the Strait of Hormuz since Thursday. He added that Lufthansa had extended the no-fly zone over Iran on Friday, without being more specific. The airline is still serving Iran's capital, Tehran.

Netherlands flag carrier KLM was no longer flying over the Strait of Hormuz, a spokesman said on Friday, while British Airways said it would adhere to the FAA guidance and use alternative routes.

Malaysia Airlines said it was avoiding the airspace, which it had previously used on flights between Kuala Lumpur and London, Jeddah and Medina.

Qantas said it was adjusting flight paths to avoid the Strait of Hormuz and Gulf of Oman until further notice. Singapore Airlines said some flights might require longer routings to avoid the area.

On Thursday, two other U.S. carriers, American Airlines and Delta Air Lines (NYSE: ), said they did not fly over Iran. Japanese carriers Japan Airlines Co Ltd and ANA Holdings Inc also said they did not fly over the area.