The US has announced a ban on large electronic devices from cabin baggage on flights from eight countries in the Middle East, North Africa and Europe.
Bombs could be hidden in laptops, tablets, cameras, DVD players and electronic games, the Department of Homeland Security (DHS) said.
The measure will affect nine airlines operating out of 10 airports. Phones are exempt from the new rules.
The UK government is introducing a similar ban on laptops.
Downing Street said airline passengers would not be able to carry laptops in cabin luggage on inbound direct flights from Turkey, Lebanon, Jordan, Egypt, Tunisia and Saudi Arabia.
The Turkish government said the US ban was wrong and should be reversed.
- Will the new US travel rules affect me?
- What about the parents?
Large electronic devices will still 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.
Which flights are affected?
The nine airlines affected by the US ban are Royal Jordanian, EgyptAir, Turkish Airlines, Saudi Arabian Airlines, Kuwait Airways, Royal Air Maroc, Qatar Airways, Emirates and Etihad Airways.
They have been given 96 hours, beginning at 07:00 GMT on Tuesday, to ban devices bigger than a mobile phone or smartphone from cabins, US officials said, adding that the ban had no end date.