US authorities have secretly required airlines from 13 nations to forbid passengers from carrying any electronic or electrical device larger than a cellphone.

No American carriers are impacted by the ban, which is coming today from the Homeland Security Department.

“Effective March 21st, the carriage of electronic and electrical devices inbound to the USA shall only be inbound in checked baggage except for mobile and medical devices,” according to a reservation agent at one of the affected airlines.

The new edict was distributed in an email described as “confidential” from the US transportation safety administration (TSA) on Monday.

 The requirement forbids passengers from bringing laptops, iPads, Kindles and even cameras larger than mobile phones into the cabin. All such devices must be checked in luggage

Saudi Arabia’s Saudia Airlines and Royal Jordanian airlines are among the affected countries; the full list has not been revealed to the affected airlines themselves.

A US official had told Reuters that the ban followed a “terrorism threat” and was expected to be announced on Tuesday.

Royal Jordanian tweeted a reference to the restrictions, referring cryptically to “concerned US departments”. It was suggested that Royal Jordanian disobeyed the circular in part by making its existence known. The airline deleted the tweet on Monday afternoon after it had been up for several hours.