Britain has stepped up security at airports after US officials said they were concerned that al Qaeda operatives in Syria and Yemen were developing bombs that could be smuggled onto planes.
"We have taken the decision to step up some of our aviation security measures," Britain's transport ministry said. "The majority of passengers should not experience significant disruption."
The United States requested tougher security at overseas airports with nonstop flights to its cities. The request came as US security sources said bombmakers from the Nusra Front, al Qaeda's affiliate in Syria, and Yemen-based al Qaeda in the Arabian Peninsula were believed to be working to develop explosives that could avoid detection by current airport screening systems.
The main concern is that militant groups could try to blow up US- or Europe-bound planes by concealing bombs on foreign fighters carrying Western passports who spent time with Islamist rebel factions in the region, the US sources said.
A spokeswoman for Britain's transport ministry declined to give any further details on the security measures or to say whether the increased security was linked to the US concerns.
Britain's Heathrow airport is the world's third busiest airport and the busiest in Europe, serving 191,200 passengers per day.