(Reuters) – The U.S. Federal Aviation Administration issued an emergency order on Thursday prohibiting U.S. operators from flying in Iran-controlled airspace over the Strait of Hormuz and Gulf of Oman due to heightened tensions.

The order came hours after United Airlines suspended flights between New Jersey’s Newark airport and the Indian financial capital of Mumbai, which fly through Iranian airspace, following a safety review after Iran shot down a high-altitude U.S. surveillance drone.

The downing of the unarmed Global Hawk aircraft, which can fly at 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.

FAA said according to flight tracking applications, the nearest civil aircraft was operating within around 45 nautical miles of a U.S. Global Hawk drone when it was shot down by an Iranian surface-to-air missile.

“There were numerous civil aviation aircraft operating in the area at the time of the intercept,” FAA said.

The agency said it remained concerned about the escalation of tension and military activity within 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.

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

“Since MH17, all countries rely on advice from the US, the UK, France and Germany to highlight airspace risk,” OPSGROUP said. “The threat of a civil aircraft shootdown in southern Iran is real.”

Flight tracking website Flightradar24 showed Qatar Airways and Emirates flights in the area prohibited for U.S. carriers at 0640 GMT on Friday. Qatar and Emirates did not respond immediately to a request for comment outside usual business hours.

Netherlands flag carrier KLM was no longer flying over the Strait of Hormuz, a spokesman said on Friday.

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

“The airline is closely monitoring the situation and is guided by various assessments including security reports and NOTAMs (notices to airmen) by respective airspace control authorities,” the Malaysian carrier said.

United said it had suspended its flights to India through Iran airspace after a “thorough safety and security review”. It 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 in order to provide our customers with the most efficient travel experience under these circumstances,” the spokesman said.

On Thursday, two other carriers, American Airlines and Delta Air Lines, 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.