Tighter security for flights to US
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".
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UK Transport Secretary Patrick McLoughlin said the measures were being taken to keep the public safe.
While he would not specify what steps would be involved, he ruled out "significant disruption" to passengers.
It comes amid US media reports that al-Qaeda affiliates in Syria and Yemen are developing bombs to smuggle on planes.
A US Department of Homeland Security (DHS) official said the changes were a response to a "real time" and "credible" threat, but he could not comment on specific intelligence matters.
'Remain vigilant'
DHS Secretary Jeh Johnson said in a statement: "We are sharing recent and relevant information with our foreign allies and are consulting the aviation industry."
The changes are expected in the coming days.
Former US secretary of state Hillary Clinton said she took the threat seriously, saying: "We have to remain vigilant."
Mr McLoughlin told the BBC that "very stringent" measures were already in place, but that the UK had to take action when given information and advice to do so.
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It is thought the measures could include more thorough screening of passengers, checks of shoes and electronic devices.
At Manchester Airport, it is believed extra swab machines were sent to departure gates on transatlantic flights to allow staff to swab hand luggage immediately before boarding, as well as at security.
The prime minister's spokesman said people should continue to fly, but advised they allow "appropriate time" to go through the tighter security.