The US Federal Aviation Administration (FAA) has banned US airlines from flying over Iraq until further notice.
The FAA said the restriction was introduced due to the “hazardous situation” created by fighting between militants from the Islamic State and Iraqi security forces.
The US launched air strikes against the Islamic State of Iraq and Levant (Isis) on Thursday.
British Airways said it was suspending flights over Iraq and would “keep the situation under review”.
Qantas has also suspended flights over Iraq, following similar action by Virgin Atlantic, Lufthansa, Emirates and Air France.
The FAA banned all air travel below 30,000 feet over Iraq on July 31.
Flying over conflict areas has come under increasing scrutiny since the apparent shooting down of Malaysia Airlines flight MH17 over Ukraine last month.
The FAA and many European carriers temporarily suspended flights to Israel’s Ben Gurion airport in Tel Aviv in July after a rocket landed nearby amid Israel’s assault on Gaza.