No airlines may fly from Turkey to the United States due to a Federal Aviation Administration order, U.S. government officials said Saturday.

“All airline carriers, regardless of country of registry, are prohibited from flying into the United States from Turkey either directly or via third country,” the U.S. Embassy in Ankara said.

In a message on its website, the Embassy warned travelers that “security at [Istanbul’s] Ataturk airport is significantly diminished.” It is, however, is open, and Turkish Airlines, the main carrier there, said Saturday that “the airport is now back to normal and flights have begun.”

The FAA has also banned any U.S. registered aircraft from flying into Turkey but that’s less of an issue for most people, as Delta, the last U.S. carrier that considered flying to Istanbul, recently suspended the service it had planned to start in May. The FAA’s ban also includes private aircraft, and that may affect some travelers.

The FAA did not say how long its ban would last.

“The FAA is monitoring the situation in Turkey in coordination with our partners in the State Department and the Department of Homeland Security and will update the restrictions as the situation evolves,” the FAA said in a statement.

The FAA’s decision is likely a bigger problem for Turkish Airlines, the global behemoth that had made U.S. flights a key part of its strategy. Like Emirates Airline, Etihad Airways and Qatar Airways, Turkish tries to capitalize on its unique location to sell Americans one-stop itineraries to hard-to-reach places, especially in Africa, the Middle East and India.

Turkish flies nonstop to Los Angeles, New York, Atlanta, Houston, San Francisco, Washington Dulles and Chicago.

On social media, passengers posted pictures of chaos at the airport, as hundreds tried to speak with airline employees.

The airline, however, said it was doing what it could. It released a statement asking passengers to go to special airline counters it was setting up in nearby hotels.