The three major US airlines halted flights with Israel after the country was attacked by Hamas over the weekend, while some Middle Eastern and European carriers continued to give passengers an exit route from the developing war. 

Delta Air Lines Inc., United Airlines Holdings Inc and American Airlines Group Inc. canceled services to Tel Aviv, as did European counterparts Deutsche Lufthansa AG, Air France-KLM and budget specialist Wizz Air Holdings Plc. 

“Operators are advised to exercise caution,” the Federal Aviation Administration said in a notice telling US airlines to review the security situation before resuming operations. “Delays are expected, operators should calculate fuel accordingly.”

In all, airlines suspended fewer than half of all flights to Tel Aviv as of Sunday, based on data from Flightradar24.com. El Al Israel Airlines, the nation’s flag carrier, expanded its schedule over the weekend to repatriate countrymen, according to Ynet News. Turkish Airlines and its local rival Pegasus also continued to offer flights, providing options for those seeking to leave. Israel declared a state of war following the surprise attack by Hamas, with fighting continuing on Monday. 

British Airways and Dubai’s Emirates and FlyDubai were among the airlines still flying to Tel Aviv on Monday. BA plans to adjust its schedule so flights leave London Heathrow in the morning rather than late afternoon, according to a spokesman. 

“That would suggest to me what they’re doing is an out-and-back crew rotation” with no stopover rest requirement, said aviation consultant John Strickland. US carriers don’t have that option because the length of the flights require a minimum 24-hour rest period, he said in an interview.

BA introduced a flexible booking policy allowing customers to change their travel dates free of charge. American Airlines, which operates a daily service to Tel Aviv from New York’s John F. Kennedy Airport, is doing the same over the coming days. Lufthansa on Monday suspended flights to Tel Aviv through Oct. 14 after a security review.

Ben Gurion International Airport in Tel Aviv typically handles about 300 departures a day, according to data on FlightRadar24. The most popular service is to Istanbul with 105 flights a week, followed by Larnaca in Cyprus and Antalya in Turkey. Dubai, Athens, Rome, Paris and Vienna are all among the top 10, the flight tracking website showed.

North American routes to Israel include Air Canada from Toronto and Montreal; Delta from New York, Boston and Atlanta; United from Washington Dulles, Newark, Chicago, and San Francisco; and American Airlines also from New York.

The UK’s Virgin Atlantic Airways Ltd. canceled some services and said its flying program to Tel Aviv remains under “constant review.”  

Airline shares dropped, with the Bloomberg World Airlines Index losing as much as 2.8%. The conflict is driving up the price of oil and thereby aviation fuel, the single-biggest expense for airlines.

Wizz slid as much as 9.4% in London, leading declines among European stocks. Its exposure to Israel is the highest among a selection of airlines tallied by analysts at Raymond James. The Hungarian carrier had several planes stuck for a time in Kyiv after war broke out with Russia. 

“They will have probably learned from that to be a bit more cautious from day one as no one really knows how this is going to go,” said Bernstein analyst Alex Irving. 

British Airways parent IAG SA dropped as much as 5.8%, while Lufthansa lost up to 4.3%. In New York, American, United and Delta each more than 5%. 

Avoiding Israeli’s relatively small airspace will add complications for airliners crossing into major hubs in the Persian Gulf and beyond. Syria to the north has remained shut to many operators for years amid the country’s civil war, while Russian and Ukrainian fly zones — constituting the biggest landmass on the planet — have also been off limits to many airlines for more than a year.

The European Union Aviation Safety Agency issued a so-called Conflict Zone Information Bulletin for Israeli air space.

“Air operators are recommended to ensure that a robust risk assessment is in place together with a high level of contingency planning for their operations and to be ready for short notice instructions from the Israeli authorities,” EASA said.

‘Not Prudent’

Several Asian carriers said they would suspend services to Israel, including Air India Ltd. and Cathay Pacific Airways Ltd., after attacks erupted around the Gaza Strip on Saturday morning. Israeli forces have hit more than 1,000 targets in Gaza, including rocket launching sites, and four combat divisions have been mobilized. 

Iberia Express is flying its two scheduled return flights to Tel Aviv on Monday, after cancellations on Saturday and maintaining flights on Sunday. The Spanish airline, also owned by IAG, introduced service to Israel in March. It will most likely flly only one return flight for the foreseeable future, according to a spokesperson.

“In the coming days we will adapt our schedule to the situation in the country and inform affected customers,” Iberia Express said on a Facebook post Sunday.

The head of American Airline’s pilots union said members shouldn’t fly to Israel until the situation is safe.

“It is not prudent or appropriate to knowingly put our flight crews and passengers in harm’s way by maintaining flights into a war zone,” Allied Pilots Association President Ed Sicher said in a statement. “I am directing all pilots to cease flight operations to Israel until we can be reasonably assured of the region’s safety and security.”

Sicher cited a US State Department travel advisory issued Sunday that said the situation in Israel is unpredictable and “mortar and rocket fire may take place without warning.”