Citing an unexplained “heightened risk of terrorism against aviation,’’ British Airways on Saturday suspended flights to Cairo for seven days.

Lufthansa, the German airline, had a one-day suspension ending Sunday.

The airlines abruptly stopped flights even as the planes were about to board, ABC News said Saturday.

Washington is not planning to follow suit, but US carriers are said to be monitoring the situation.

Britain also advised its citizens to cancel “all but essential travel’’ to Egypt’s Sinai Peninsula.