Large electronic devices have been banned from cabin baggage on US flights from eight Muslim-majority countries.
According to the Department of Homeland Security (DHS), bombs could be hidden in laptops, tablets, cameras, DVD players and electronic games.
The measure will affect nine airlines operating out of 10 airports. Phones are exempt from the new rules.
The Turkish government said the ban was wrong and should be reversed.
Large electronic devices will only be allowed on board in checked baggage.
Passengers on some 50 flights a day from some of the busiest hubs in the Middle East, Turkey and North Africa will be required to follow the new rules.
The nine airlines affected are Emirates and Etihad Airways, Qatar Airways, Royal Jordanian, Egypt Air, Turkish Airlines, Saudi Arabian Airlines, Kuwait Airways, Royal Air Maroc.
On March 21, they have been given 96 hours, beginning at 07:00 GMT, to ban devices bigger than a mobile phone or smartphone from cabins, US officials said, adding that the ban had no end date.
The airports affected are:
- Mohammed V International, Casablanca, Morocco
- Ataturk Airport, Istanbul, Turkey
- Cairo International Airport, Egypt
- Queen Alia International, Amman, Jordan
- King Abdulaziz International, Jeddah, Saudi Arabia
- King Khalid International, Riyadh, Saudi Arabia
- Kuwait International Airport
- Hamad International, Doha, Qatar
- Abu Dhabi International, United Arab Emirates
- Dubai International, United Arab Emirates
EgyptAir said it would start implementing the ban as of March 24.
The Middle Eastern and North African airports affected are nearly all ones with close, friendly relations with Washington, so this will be seen by some as a drastic and unpopular measure. Wealthy Gulf Arab business leaders flying to the US, for example, will no longer be able to work on their laptops mid-flight.
However, aviation security experts were alarmed by an incident in Somalia last year when the insurgent group al-Shabaab smuggled an explosive-filled laptop on a flight out of Mogadishu, blowing a hole in the side of the plane. The aircraft was still low enough that the pilot was able to land the plane safely.
In a statement, the DHS said: “The US government is concerned about terrorists’ ongoing interest in targeting commercial aviation, including transportation hubs over the past two years, as evidenced by the 2015 airliner downing in Egypt; the 2016 attempted airliner downing in Somalia; and the 2016 armed attacks against airports in Brussels and Istanbul.
“Evaluated intelligence indicates that terrorist groups continue to target commercial aviation, to include smuggling explosive devices in various consumer items.”
Homeland Security Secretary John Kelly called members of Congress over the weekend to explain the security issues behind the ban, congressional aides said.
The restrictions are said to have been under consideration for several weeks.