Security is being tightened at airports with direct flights into the US - including some in the UK - in response to US warnings of a "credible threat".
The UK transport department confirmed airport security was being stepped up.
Neither UK nor US authorities specified what new measures would be involved but the UK said most passengers should not experience "significant disruption".
It comes amid US media reports that al-Qaeda affiliates in Syria and Yemen are developing bombs to smuggle on planes.
— Channel 4 News (@Channel4News) July 3, 2014
A US Department of Homeland Security (DHS) official said the changes were a response to a "real time" and "credible" threat but it could not comment on specific intelligence matters.
"Aviation remains an attractive target to global terrorists, who are consistently looking for ways to circumvent our aviation security measures.
"As always, DHS continues to adjust security measures to fit an ever evolving threat environment.
"Information about specific enhancements and locations are sensitive as we do not wish to divulge information about specific layers of security to those who would do us harm."
The UK government isn't giving any details about what these security changes actually are, but they haven't ruled out longer queues at security.
The statement from the department for transport merely says that the majority of passengers should not experience significant disruption.
What we do know is that all of the old rules remain in place. So you will still have to put liquids into separate, see-through bags, take your laptop out of your bag, take off your belt and maybe your shoes before going through security.
It's also not clear whether these changes will affect every airport, and whether they are limited to flights to and from the United States, which has prompted this move.
The actual terrorism threat level remains the same, at substantial. That's the middle of the five threat levels and means that an attack is a strong possibility.
DHS Secretary Jeh Johnson said in a statement: "We will work to ensure these necessary steps pose as few disruptions to travellers as possible,"
MORE: Sources: DHS directives expected to require expanded screenings if airlines want to fly planes into US: http://t.co/EcUxjMTA1v
— ABC News (@ABC) July 2, 2014
"We are sharing recent and relevant information with our foreign allies and are consulting the aviation industry."
The changes will be made in the "upcoming days", the department added.
In a statement, the UK Department for Transport said the country had "taken the decision to step up some of our aviation security measures".
He added: "For obvious reasons we will not be commenting in detail on those changes. The majority of passengers should not experience significant disruption."
An anonymous US official told Reuters news agency that European airports would be taking the extra precautions.
Law enforcement and security officials sources told the news agency that Western authorities were discussing security measures that included extra scrutiny of US-bound passengers' electronics and footwear, among other measures.
Al-Nusra Front, al-Qaeda's affiliate in Syria, and Yemen-based al-Qaeda in the Arabian Peninsula are believed to be working together to try to develop explosives that could avoid detection by current airport scanners, US media report.