Britain pointed the finger at shortcomings in Egyptian airport security on Tuesday after blaming last month's Russian plane crash on a bomb smuggled on board.
Foreign Secretary Philip Hammond said the most likely cause of the disaster was a bomb planted by someone working for or inspired by the Islamic State group.
But, he said Tuesday, failures in security at Sharm El-Sheikh airport may have enabled the first successful bombing of a jet since the 1988 Lockerbie attack.
"I don't really think there's anyone left around who doesn't recognize that this is more than likely a bomb," Hammond told reporters in Washington.
"You don't need a sophisticated capability to get a small bomb, and that's all you need to bring down an aircraft, a small bomb with a straightforward timer.
"Sadly there are many, many people who can do that. The issue is about getting it air side in an airport that is supposed to be secure," he warned.
"Where this points the finger is at the capability of the security on the ground at Sharm El-Sheikh."
Hammond said Britain sent a security team to the airport in the immediate aftermath of the October 31 crash that had killed all 224 mainly-Russian people on board.
"They looked back on CCTV footage of the search areas and things over the previous couple of days," he said.
"On the basis of what we saw we decided that we had to stop flying until we'd sorted out, until the Egyptians had sorted it out," he added.
Britain has begun flying thousands of tourists home from the Egyptian resort, but there have been delays as they are screened and separated from their luggage.
Amid fears that other attacks might have been planned, passenger baggage is being searched separately and flown home by cargo jet.
In comments that may further anger Egyptian officials, Hammond suggested some countries have a problem with training and motivation of security staff.
"There's a cultural problem here, and I'm not pointing the finger at the Egyptians -- this is the case in a large part of the world," he said.
"There'll be countries in this hemisphere that suffer from it as well: The idea that security is about installing some new machines and writing up a manual."
Instead, he said, the problem was properly training airport staff to be attentive to the risks.
The minister said that after the immediate crisis is past Britain could work with Egypt to improve procedures, but the priority is getting Britons home.