British Airways has cancelled all flights to the Egyptian capital Cairo for a week as a security "precaution".
Passengers about to board a BA flight to the city from London's Heathrow Airport were told that it was cancelled - and that there would be no alternative flights for a week.
The airline did not specify what the security issue was.
A spokesman for Cairo airport told the BBC the airport had yet to be notified by BA of any such changes.
A BA spokesman said: "We constantly review our security arrangements at all our airports around the world, and have suspended flights to Cairo for seven days as a precaution to allow for further assessment.
"The safety and security of our customers and crew is always our priority, and we would never operate an aircraft unless it was safe to do so."
Christine Shelbourne, 70, from Surrey was due to go to Cairo for a week with her 11-year-old grandson. She said she managed to check into the flight. However, her boarding card wouldn't open the barriers.
She said: "The check-in staff reissued my boarding pass and I tried again but that didn't work either and we were told to try again in half an hour.
"Whether they knew anything I don't know but my husband told me the flight had been cancelled before they did. There were no suggestions or help from staff about alternative flights."
"My 11-year-old grandson is heartbroken - he's been looking forward to the trip for months. We're just not going now," she added.
"It was handled badly to be honest. My grandson is currently looking for flights for us - he's devastated."
The UK Foreign Office on Friday updated its advice for Britons travelling to Egypt.
The advice includes the warning: "There's a heightened risk of terrorism against aviation. Additional security measures are in place for flights departing from Egypt to the UK."
All other airlines that use the airport are operating normally, a BBC reporter based in Cairo said.
Following the bomb explosion that destroyed a Russian airliner over Egypt's Sinai peninsula in October 2015 after it had departed Sharm El Sheikh airport, the UK was one of a number of countries to temporarily suspend flights to and from the country.
The Foreign Office continues to advise against travel to certain parts of Egypt.