Airline passengers travelling to the UK from six countries in the Middle East and north Africa are to be banned from carrying laptops and other large electronic devices as cabin luggage.
Downing Street announced that the ban affects direct inbound flights from Turkey, Lebanon, Jordan, Egypt, Tunisia and Saudi Arabia.
It covers devices which are larger than a typical smartphone measuring 16cm by 9.3cm by 1.5cm, which will now have to go in the plane's hold.
The move was ordered by Prime Minister Theresa May in the latest of a series of meetings on aviation security.
Affected airlines were informed immediately, but may take a few days to implement the new security measure, a spokesperson for Mrs May said.
It follows a similar measure announced by the US authorities affecting flights originating in a longer list of eight mainly Muslim countries.
Mrs May's official spokesman declined to discuss whether the new rules were prompted by specific intelligence, while the US government cited unspecified "threats".
The tightening of security comes just weeks after it was revealed that UK security services have foiled 13 potential attacks in less than four years, while counter-terrorism units are running more than 500 investigations at any time.
No similar change planned for Ireland - Dept
The measures are not likely to be adopted in Ireland, according to the Department of Transport.
"Aviation security in Ireland is governed primarily by EU rules and regulations and Ireland complies with the EU's common security standards," said a spokesperson for the Department of Transport.
"Security measures at Irish airports have not changed nor are they expected to change in the near future."
Statement from the Irish Aviation Authority said: "The US directive does not affect any Irish airports, any Irish registered airlines or any airlines operating to/from Ireland contained on the US directive list."
The situation will be kept under review, it added.
UK, US changes come amid terror threats
In an earlier security measure introduced in July 2014, passengers at UK airports were advised to ensure electronic devices were charged so they could be switched on or face not being allowed to take them onto aircraft.
The move came amid reports two terror networks were working together on a bomb that could evade existing measures.
Announcing the new restrictions, a government spokesman said: "The safety and security of the travelling public is our highest priority.
"That is why we keep our aviation security under constant review and put in place measures we believe are necessary, effective and proportionate.
"The additional security measures may cause some disruption for passengers and flights, and we understand the frustration that will cause, but our top priority will always be to maintain the safety of British nationals.
"Decisions to make changes to our aviation security regime are never taken lightly. We will not hesitate to act in order to maintain the safety of the travelling public and we will work closely with our international partners to minimise any disruption these new measures may cause."
Britain has been in close touch with the US authorities over the issue, the spokesman said.
Asked why the US ban, affecting 10 named airports in eight countries, differs from that imposed by the UK, he told reporters: "We have each taken our own decisions. Our decisions are for us."
UK airlines operating direct flights which will be hit by the new measures are British Airways, easyJet, Jet2.com, Monarch, Thomas Cook and Thomson, while overseas airlines affected are Turkish Airlines, Pegasus Airways, Atlas-Global Airlines, Middle East Airlines, EgyptAir, Royal Jordanian, Tunis Air and Saudia.
The official threat level for international terrorism has stood at severe, meaning an attack is "highly likely", for more than two years.
US president Donald Trump has attempted to introduce a travel ban aimed at people from Muslim-majority countries, which has run into trouble in the US courts.
