Israel briefly reopened its airspace on Sunday and is expanding flight operations on Monday, aiming to help tens of thousands of travellers stranded by widespread cancellations across the Middle East after the U.S. attacked Iran, Reuters reported.

An organisation that monitors flight risks warned on Sunday that U.S. strikes on Iran's nuclear sites could heighten the threat to American operators in the region.

With Russian and Ukrainian airspace also closed due to war, the Middle East has become a more important route for flights between Europe and Asia, but flight tracking website FlightRadar24 showed empty space over Iran, Iraq, Syria and Israel. Airlines have chosen routings such as north via the Caspian Sea or south via Egypt and Saudi Arabia, even if these mean higher fuel and crew costs and longer flight times, according to Reuters.