International airlines have begun avoiding flying over the Strait of Hormuz and the Gulf of Oman.

Several international airlines said Friday that they had begun diverting flights to avoid some of the airspace over the Strait of Hormuz and the Gulf of Oman, where Iran shot down a U.S. drone a day earlier. The incident sparked concerns over a military escalation, as President Donald Trump initially ordered a retaliatory attack against Iran, even though he later called it off.

The downing of the U.S. military surveillance drone by Iran occurred in airspace frequently used for international flights, and the Federal Aviation Administration said there "were numerous civil aviation aircraft operating in the area at the time of the intercept." Airlines including Emirates, Qatar Airways and Etihad Airways are headquartered near the Strait of Hormuz.

Amid concerns that possible future strikes could accidentally hit and down commercial aircraft, the FAA issued an emergency order for the region, citing the possibility of "miscalculation or misidentification." The order bans only U.S. carriers from the area and does not require that foreign carriers take action, but the agency's advice is often heeded abroad.

An independent safety guidance company, OpsGroup, was more explicit, writing: "The Threat Of A Civil Aircraft Shootdown In Southern Iran Is Real." Dutch airline KLM, Singapore and Malaysia Airlines, Germany's Lufthansa, Emirates, Fly Dubai, and Australia's Qantas were among the carriers that subsequently said they would divert flights until further notice. The areas avoided by those airlines appeared to slightly differ, and in some cases, it was not immediately clear when the changes would take effect.

The warnings Friday were a stark reminder of the 2014 downing of Malaysia Airlines Flight 17 over eastern Ukraine, in which 298 people were killed. Five years after the Kuala Lumpur-bound flight was shot down, Dutch prosecutors named four suspects Wednesday believed to be responsible for the incident - an announcement that served as a reminder of the risks of operating flights over conflict zones. The Dutch-led investigation concluded that the missile system used to down MH17 was moved into eastern Ukraine from Russia and may have accidentally targeted the commercial flight. Forces on the ground, the investigators concluded, may have mistaken MH17 for a Ukrainian military plane.

On Friday, OpsGroup compared the Russian missile system that was used to down MH17 to the system that brought down the U.S. surveillance drone Thursday. "Any error in that system could cause it to find another target nearby - another reason not to be anywhere near this part of the Straits of Hormuz," the company warned.

Thursday's incident and the varying responses from global airlines highlighted an ongoing debate over the lessons that should be learned from the MH17 downing.

Some safety analysts have argued that flights over conflict zones or areas of likely conflict should be entirely banned to avoid an MH17 repeat. Individual countries can already close parts of their own airspace, and regional bodies such as the FAA are able to exert such influence over carriers based in their own jurisdiction. But so far, there is no body with the authority to do so globally.

There also remains disagreement over what exactly constitutes a conflict that requires immediate action. The most expansive definition would see large parts of the airspace over the Middle East and parts of Africa banned. Airlines have countered that case-by-case decisions remain their preferred option.

Besides the Dutch-led efforts to establish responsibility for the downing, a separate Dutch body was tasked after the 2014 incident with examining how airlines' decision-making process on costly diversions could be improved to provide maximum safety.

The Dutch Safety Board eventually issued 11 recommendations, including an encouragement to "share more information about conflicts that pose a risk to civil aviation."

In a follow-up report published in February, the Safety Board acknowledged global improvement and wrote that "stakeholders no longer assume that open airspace over a conflict zone actually guarantees safe passage. Airlines are taking a more structured approach to analyzing the risks and uncertainties, scaling up to a higher risk level at an earlier stage." Global airlines now regularly look for advice from U.S. authorities, but also from French, German and British officials, to divert their flights.

But Thursday's drone downing and the subsequent responses revealed lingering vulnerabilities. The FAA had issued a warning concerning flights in the region a month ago, citing the potential risk of Iranian antiaircraft missiles, but Lufthansa, Qantas and KLM were still operating flights in the area by early Thursday.

Other airlines continued to operate in the area even Friday, according to Reuters - a situation that echoed the different assessments airlines reached during the eastern Ukraine conflict in 2014.

British Airways and Qantas were among the airlines that had avoided the area for months by July 17, 2014, citing safety risks. Malaysia Airlines had come to a different conclusion.