British Airways and Lufthansa abruptly suspended flights to Cairo from Saturday over security concerns, but gave no details about what may have prompted the move.

"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," British Airways said in a statement.

Lufthansa later said it had canceled its flights to Cairo on Saturday from Munich and Frankfurt and will resume its flights on Sunday

British Airways, a unit of IAG, said that it would never operate an aircraft unless it was safe to do so. When asked for more details about why flights had been suspended and what security arrangements the airline was reviewing, a spokeswoman responded: "We never discuss matters of security."

Three Egyptian airport security sources told Reuters that British staff had been checking security at Cairo airport on Wednesday and Thursday. They gave no further details.

The British Foreign Office updated its travel advisory on Saturday to add a reference to the British Airways' suspension, advising travelers affected to contact the airline.

Egypt's Ministry of Civil Aviation said in a statement late on Saturday that it had contacted the British Embassy in Cairo, which had confirmed that the decision to suspend the flights was not issued by Britain's transport or foreign ministries.

The Egyptian ministry added that it will add more flights from Cairo to London starting on Sunday "to facilitate transporting passengers during this period."

The British government has long advised against all but essential travel by air to and from the Egyptian resort of Sharm el-Sheikh, where a Russian passenger jet was bombed in 2015, but has not issued similar warnings against air travel to and from Cairo.

"There's a heightened risk of terrorism against aviation. Additional security measures are in place for flights departing from Egypt to the UK," the British advisory says.