The U.S. government told airlines flying over Iraq to remain at higher altitudes, amid growing concerns about carriers operating around conflict zones.

U.S. airlines are now prohibited from flying over Iraq below 30,000 feet, the Federal Aviation Administration said. The agency, which had previously restricted airlines from flying below 20,000, issued the new requirement because of "the potentially hazardous situation created by the armed conflict in Iraq."

The guidance, which is mandatory for all U.S. airlines but not others, comes amid increased disquiet about airlines flying near conflict zones after thedowning of Malaysia Airlines Flight 17 over war-torn eastern Ukraine.

The Malaysia Airlines Boeing jetliner was flying at 33,000 feet in airspace the Ukrainian government had said was safe when it was shot down by a suspected antiaircraft missile fired by pro-Russia separatist rebels. Russia denies the rebels downed the plane.

Some airlines have already opted to avoid Iraqi airspace altogether. European aviation safety regulators on Friday issued their own nonbinding safety bulletin on the country.

Air France said this week it stopped flying over Iraq, and Deutsche Lufthansa AG said late Friday it would suspend overflights and halt operations to the northern city of Erbil.