Britain's advisory to its airlines to avoid Lebanon's airspace came hours after Egypt instructed all of its airlines to avoid Iran's airspace for three hours in the early morning on Thursday.
Many airlines globally are revising their schedules to avoid Iranian and Lebanese airspace while also calling off flights to Israel and Lebanon.
Flights through conflict zones became a prominent industry safety issue a decade ago after Malaysia Airlines flight MH17 was shot down over Ukraine, killing all 298 people on board.