Major airlines shunned Israel for a second day on Wednesday amid fears that rocket fire from Gaza could endanger flights into Tel Aviv's Ben Gurion airport.
In Washington, officials renewed a formal ban on American flights to Israel until 1615 GMT on Thursday, and around the world many other airlines took their own precautions.
Previous conflicts in Gaza, which is under assault by Israeli forces trying to halt Palestinian rocket fire, have not endangered civilian flights in Israeli airspace.
But the cancellations highlighted increased fears for passenger aviation in the wake of last week's downing of a Malaysia Airlines Boeing 777 over Ukraine with almost 300 on board
The Federal Aviation Administration issued its ban on Tuesday after a rocket fell on a neighborhood to the north of Ben Gurion, raising fears that a commercial flight could be struck.
But US Secretary State John Kerry did land in Israel, and the State Department said that his team "were very comfortable" despite the rocket threat.
"Hamas does have rockets that can reach Ben Gurion airport… although the accuracy of their rockets does remain limited," State Department spokeswoman Marie Harf said.
Delta, United and US Airways all cancelled their scheduled flights for Wednesday, as did a raft of European carriers including Germany's Lufthansa, Air France, Poland's LOT and others.
"We will continue to suspend flying to and from Tel Aviv ... and will continue to coordinate with the FAA to ensure the safety of our customers and employees," a United spokeswoman said.
"We plan these things conservatively," added US carrier Delta's chief executive Richard Anderson, speaking on the CNBC business news cable channel.
"But we will need concrete information from our government that lets us draw an independent conclusion ... that it's going to be safe for our passengers and our employees."
Austrian Airlines, Brussels Airlines, Finnair, Iberia, Lufthansa, Air Berlin, Aegean and SAS cancelled services to Tel Aviv. British Airways flights continued.
"At the moment there is no reliable new information that would justify a resumption of flight service," said Lufthansa in a statement.
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Austrian, which carries up to 700 passengers between Vienna and Tel Aviv every day, and SAS said they would review the situation for Thursday.
Aeroflot and Romanian carrier TAROM, on the other hand, said they would resume flights Wednesday after cancelling Tuesday. Air Canada cancelled one flight on Wednesday and another Thursday.
The FAA said it was "working closely" with Israel to "determine whether potential risks to US civil aviation are mitigated so the agency can resolve concerns as quickly as possible."
Meanwhile, Israeli flag carrier El Al declared on its website that it was business as usual.
"In light of flight cancelations to Israel by foreign air carriers we would like to inform you that El Al, as always, will continue to fly from and to Israel," it told travellers.
"The company will continue to keep Israel's skies open, and will be at your service at any time," it said in a post that it headlined: "Always here, always will be."
Passengers on an El Al flight out of New York on Tuesday included the city's billionaire former mayor Michael Bloomberg, in what he said was a show of solidarity with Israel.
Bloomberg called Ben Gurion the "best protected airport in the world" where El Al flights had continued safely despite the European and North American cancellations.
"The flight restrictions are a mistake that hands Hamas an undeserved victory and should be lifted immediately," he said.
"I strongly urge the FAA to reverse course and permit US airlines to fly to Israel."
Israel called American air carriers Tuesday to assure them there was no security problem for take-offs and landings.
Kerry, who is trying to broker a ceasefire in Gaza, told Israeli Prime Minister Benjamin Netanyahu the FAA ban was ordered only to protect the safety of US citizens.
The Israeli Airports Authority meanwhile announced it would open the Ovda military airport, 35 miles (60 kilometers) north of Israel's Red Sea resort of Eilat, as an alternative to Ben Gurion.