Multiple cities in Iran were hit by missiles, while counterstrikes targeted US bases in Bahrain, Qatar, the UAE and Kuwait – as well as sites in Israel.
British Airways said it had cancelled flights to Tel Aviv and Bahrain up to 3 March, as well as Saturday’s Amman, Abu Dhabi, Dubai, and Doha services.
It told Sky News that customers would be able to change their flights for free.
One BA flight from London to Doha, Qatar‘s capital, was earlier forced to turn around mid-flight, according to flight tracking websites.
London Heathrow said “a small number of flights” had been cancelled or delayed and advised travellers to check with their airline.
Its departures board showed cancellations, including an Emirates flight to Dubai, a Qatar Airways flight to Doha, and an Etihad service to Abu Dhabi.
A Gatwick spokesperson said it was also “expecting disruption to our Qatar and Emirates flights”.
Manchester Airport departures showed a Saturday night Emirates flight to Dubai had been scrapped and it shared a Civil Aviation Authority post telling people to check with their airline.
Wizz Air also confirmed flights between London Luton to Tel Aviv, in both directions, were suspended until 7 March, but that “operational decisions will continue to be reviewed”.
Virgin Atlantic said routes from destinations including India and the Maldives would be altered for safety reasons, meaning journeys could take longer.
Many other international airlines have also paused flights to the Middle East, as well as some routes flying over the region, including Delta, Lufthansa, Cathay Pacific and Turkish Airlines.
India’s airlines are also suffering serious disruption due to the crisis on its doorstep.
Its aviation ministry said more than 400 flights by domestic carriers had been cancelled on Saturday and a similar number are expected on Sunday.
At least 90,000 people transfer every day in Dubai, Doha or Abu Dhabi on just three airlines, Emirates, Qatar Airways and Etihad Airways, according to analytics firm Cirium.
People in Dubai were earlier filmed running for shelter as air raid sirens sounded and witnesses told Reuters at least three big blasts were heard over the city.
Qatar’s international airport also suspended all services after the country’s airspace was shut down.
Video showed people running for cover as a missile – which was likely intercepted – fell into a residential area in its capital, Doha.
America’s largest regional air base, al Udeid, is near the city and Iran has deemed all US bases in the region as fair game.