(FOX NEWS) — Jet fuel prices in the U.S. have more than doubled in a matter of weeks as Middle East tensions squeeze supply, fueling concerns airlines could run short of fuel.

Prices jumped from about $2.17 to $4.56 per gallon by March 20, according to the Argus U.S. Jet Fuel Index. Airlines warn inventories could run dry within weeks, raising the risk of higher airfares and flight cancellations.

Airlines are already adjusting. United Airlines CEO Scott Kirby said the carrier will cut about 5% of planned flights in the near term as fuel costs surge, warning that if prices persist, jet fuel alone could add $11 billion in annual expenses.

United is also scaling back service during off-peak periods and suspending select international routes, including Israel and Dubai due to the conflict.

Meanwhile, Delta Air Lines CEO Ed Bastian said on Tuesday the jet fuel spike added as much as $400 million in costs in March alone. Speaking at a J.P. Morgan industrial conference, Bastian said airlines are moving quickly to pass those higher costs on through fare increases.

American Airlines expects fuel to add about $400 million to its first-quarter expenses.