The U.S. and Britain are banning large carry-on electronics from direct flights from several countries in the Middle East and North Africa as of Saturday, while Canada is still considering a similar decision.

The U.S. was the first to announce the new restrictions on Tuesday, saying they applied to planes coming directly from 10 airports in the Middle East and North Africa in response to unspecified security threats.

Later Tuesday, Britain announced similar restrictions on direct flights from Turkey, Lebanon, Jordan, Egypt, Tunisia and Saudi Arabia for the safety of the public, a spokesperson for Prime Minister Theresa May said.

"Direct flights to the U.K. from these destinations continue to operate to the U.K., subject to these new measures being in place," May's spokesperson told reporters. "We think these steps are necessary and proportionate to allow passengers to travel safely."

Important notice to our passengers who are traveling to USA <a href="https://twitter.com/hashtag/EGYPTAIR?src=hash">#EGYPTAIR</a> <a href="https://t.co/qAVC04B6sf">pic.twitter.com/qAVC04B6sf</a> —@EGYPTAIR

For flights into the U.K., passengers would not be allowed to bring phones, laptops or tablets into the cabin if they measure over 16 centimetres in length and 9.3 centimetres in width, with a depth of over 1.5 centimetres. Larger items would have to be checked as baggage and carried in the hold, he said.

The U.S. has only said the restricted items can't be "larger than a cellphone/smartphone."

Canadian Transportation Minister Marc Garneau said Canada is reviewing the information, but has not made a similar decision.

"Canada makes its own decisions," said Garneau. "We'll see."

A statement from Transport Canada said the government is "in close contact with U.S. security officials," but wouldn't go into detail about security concerns.

The statement added that a decision on a similar ban will be made "shortly."

Senior officials in U.S. President Donald Trump's administration announced the restrictions Tuesday morning.

The officials said the decision was prompted by intelligence about potential threats to airplanes bound for the United States. The officials would not discuss the timing of the intelligence report or if any particular group is thought to be planning an attack.

Airlines will have until 3 a.m. ET Saturday to implement the policy or face being barred from flying to the United States, the officials said, though some airlines have said they will begin enforcing the ban sooner.

The U.K. ban affects direct flights from six countries, while the U.S. ban affects flights from international airports in the following 10 cities:

Amman, Jordan.

Kuwait City, Kuwait.

Cairo.

Istanbul.

Jeddah and Riyadh, Saudi Arabia.

Casablanca, Morocco.

Doha, Qatar.

Dubai and Abu Dhabi, United Arab Emirates.

About 50 flights a day to the U.S., all on foreign carriers, will be affected. The officials said no U.S.-based airlines have non-stop flights from those cities to the United States.

So far, one flight to Canada is known to be affected. Royal Jordanian airlines said in a statement that a flight from Amman, Jordan, to Montreal will be under the ban because the flight is combined with one to Detroit.

Attention all passengers ⚠️ <a href="https://t.co/HCNDcjcdi1">pic.twitter.com/HCNDcjcdi1</a> —@RoyalJordanian

Medical devices excluded

A spokesperson for the UAE-based Emirates airline, the largest airline in the Middle East, confirmed to CBC News that the directive has been issued, saying it excludes medical devices.

The new restrictions apply to many electronic devices in the carry-on bags of passengers travelling to the U.K. and the U.S. (Chris Ison/Associated Press)

"It is applicable to all U.S.-bound passengers from Dubai International Airport, whether originating or transiting through. Emirates requests that all passengers travelling to the U.S. pack all electronic devices larger than a cellphone/smartphone in their checked-in baggage," the spokesperson said.

The spokesperson said the directive will stay in place until Oct. 14.

However, U.S. Homeland Security said the new rules will "remain in place until the threat changes."

The U.S. ban applies to 10 cities in eight countries. The U.K. ban affects six countries. (CBC)

Threats 'very clear'

Bennet Waters, principal at the Chertoff Group, a Washington consulting firm, and a former senior official at the Homeland Security Department, said Tuesday that threats to commercial aircraft have been evolving since before the Sept. 11, 2001, attacks.

He said when he was in the government, the threat to aircraft was "very clear, very consistent and it was very persistent."

The new U.S. and British rules for electronics appear to address an evolving threat. The targeted airports are in a region where the terror threat has been elevated for several years.

The 10 airports singled out by the U.S. may have been selected because screening equipment and procedures for carry-on luggage may not be effective enough to detect certain types of non-metallic explosive devices. Waters said screening of checked bags is often more intensive.

The ban would begin just before next Wednesday's meeting of the U.S.-led coalition against ISIS in Washington. A number of top Arab officials were expected to attend the State Department gathering. It was unclear whether their travel plans were related to any increased worry about security threats.

Homeland Security Secretary John Kelly phoned lawmakers over the weekend to brief them on aviation security issues that have prompted the impending electronics ban, according to a congressional aide briefed on the discussion. The aide was not authorized to speak publicly about the issue and spoke on the condition of anonymity.

Most major airports in the United States have a computer tomography or CT scanner for checked baggage, which creates a detailed picture of a bag's contents. They can warn an operator of potentially dangerous material, and may provide better security than the X-ray machines used to screen passengers and their carry-on bags. All checked baggage must be screened for explosives.