A U.S. ban on laptops and tablets in cabins of trans-Atlantic flights to the United States appeared all but inevitable Friday after Department of Homeland Security officials briefed European governments on a proposal that would affect millions of passengers.

The move, which would impact routes that carry as many as 65 million people a year on over 400 daily flights, would expand a ban already in place for planes flying out of eight Middle Easte and African countries.

The restriction was introduced in March over fears that bombs or explosive materials could be concealed on electronic devices brought onboard. Cellphones would still be allowed in cabins but virtually every other electronic device would not be permitted and would need to be stowed in checked bags.

One issue that has become a focus for security officials is how to make sure that lithium batteries used in laptops aren't turned into bombs that can be detonated mid-air even if stored in luggage holds.

The United Kingdom has a similar ban in place for some in-bound flights, although its list of targeted countries differs from that of the United States.

Officials from France, Britain, Germany, Spain and Italy took part in the conference call Friday with the U.S. Department of Homeland Security.

A French official who was briefed about the talks said the Americans announced they wanted to extend the current ban, and the Europeans planned to formulate a response in coming days, according to the Associated Press. The official, who spoke on condition of anonymity to discuss the plan, said the primary questions revolved around when and how — not whether — the ban would be imposed.

Jenny Burke, a Homeland Security spokeswoman, said no final decision has been made on expanding the restriction. But Homeland Security officials met Thursday with high-ranking executives of the three leading U.S. airlines — American, Delta and United — and the industry’s leading U.S. trade group, Airlines for America, to discuss expanding the laptop policy to flights arriving from Europe.

Two airline officials briefed on the discussions said DHS gave no timetable for an announcement, but they were resigned to its inevitability. They spoke to the AP on condition of anonymity because they were not authorized to discuss the meeting publicly.

U.S. airlines say they still hope to have a say in how the policy is put into effect at airports to minimize inconvenience to passengers.

The current ban, which affects about 50 flights per day from 10 cities, does not prevent passengers from checking laptops and other electronic devices into luggage holds.

Still, the move could lead to fewer bookings and would complicate passengers' travel plans. The U.S. is a major destination for Europe-originated flights, with more than 10 million travelers flying there each year from destinations across the continent.

Caroline Bremner, head of travel at research firm Euromonitor International, said that before President Trump took office the U.S. was expected to see 85.2 million airline passenger arrivals by 2020. Under the new administration, arrivals to the U.S. are forecast to drop slightly to 84.2 million for the period.