Most of the largest U.S. airlines said Friday they will temporarily reduce service to Mexico, as swine flu fears keeps many U.S. travelers from venturing south of the border.

Continental Airlines Inc., the biggest U.S. carrier to Mexico, said it will cut by half the number of seats it sells to fly to Mexico beginning Monday. The Houston-based airline said it will work with travelers to get them where they need to go, although schedules and routes might change.

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US Airways Group Inc., another major U.S. carrier to Mexico, said it would reduce its May and June departures to Mexico by 38 percent, beginning May 10.

Delta Air Lines Inc. also said it would reduce its Mexico service to match declining demand, but it didn't indicate how deep the cuts would be.

UAL Corp.'s United Airlines said it will cut its weekly flights to Mexico from 61 to 24 this month, beginning on Tuesday. Its June schedule will drop from 90 flights per week to 52. United said Mexico represents less than 2 percent of its overall capacity.

Southwest Airlines Co. doesn't fly to Mexico, but its chief executive said bookings within the U.S. may have softened in the past week in response to concern about flying.

"It's having an effect on air travel," Southwest CEO Gary Kelly told The Associated Press. "The bookings this week have been erratic at best ... it does seem like we're off-trend, and I just wouldn't be surprised at all if we find that our traffic is impacted over the next couple of weeks because of this concern."

Kelly didn't provide any numbers, but he said that as schools close — Fort Worth became the first large U.S. district to shut all its campuses — and large public events around the country are canceled to avoid spreading the virus, air traffic could fall.

Continental said it will reduce May flights to Mexico by about 40 percent and use smaller planes but will continue flying to all 29 Mexican cities it serves. It also extended its waiver policy to let customers with trips booked for Mexico change itineraries without penalty by the end of May.

Continental was running an average of 450 flights a week to Mexico, and the changes will cut its expected May capacity about 2 percent.

"We were already experiencing soft market conditions due to the economy, and now our Mexico routes in particular have extra weakness," said Larry Kellner, Continental's chairman and CEO.

US Airways said it would reduce its schedule by cutting the number of flights and by flying smaller planes, but that it wouldn't pull out of any Mexican cities altogether.

It also said it would reevaluate its July and August schedule in the next few weeks. It said it hopes to resume its normal schedule of flights to Mexico on July 2.

US Airways said the planned reductions amount to 0.5 percent of its systemwide departures.

Jim Corridore, an analyst for Standard & Poor's, said the reductions are an insignificant part of Continental's total capacity and revenue, and it's an even smaller problem for other airlines.

"If the main concern stays focused on Mexico, swine flu shouldn't have a big impact on the U.S. airline industry," he said. "I would expect that this would be a short-term issue."

Delta officials said they were reducing flight frequencies and switching to smaller jets on some flights to pare capacity to Mexico while still serving 11 Mexican cities. Atlanta-based Delta, which also operates Northwest Airlines, runs 350 flights a week to Mexico.

AirTran Airways, which operates only 16 weekly flights to the resort town of Cancun, will cut two of those flights. Spokesman Christopher White said the decision was based on demand over the past several weeks, not just since the flu epidemic hit.

JetBlue Airways Corp. canceled about a dozen flights over the next month to Cancun because they weren't full enough, said spokesman Bryan Baldwin.

American Airlines was monitoring travel demand to Mexico but hadn't canceled any flights by late afternoon, said spokesman Tim Smith. AMR Corp.'s American is the second-biggest U.S. carrier to Mexico.

Health authorities have confirmed 15 swine-flu deaths in Mexico and one in the U.S., a toddler from Mexico who died this week in Houston. There are more than 500 confirmed cases worldwide, including more than 300 in Mexico and more than 100 in the U.S.

A United Airlines ramp worker in Denver was among those confirmed with swine flu, said airline spokesman Rahsaan Johnson. The man last worked on April 23, and reported getting sick after that, Johnson said. There's been no indication that any of the man's co-workers have fallen ill, he said.

"We're all very happy that he is well. He is out of the hospital and recovering. We are looking forward to welcoming him back to work," Johnson said.

The U.S. Centers for Disease Control and Prevention advised against nonessential travel to Mexico, and European Union officials advised their citizens to postpone nonessential travel to parts of Mexico and the U.S. affected by swine flu.

A check by The Associated Press on Wednesday showed that some flights from the United States to Mexico had an unusually high number of empty seats. Flights heading north appeared to be fuller.

After a flap this week over comments by Vice President Joe Biden, who said he told family members to avoid airplanes, Transportation Secretary Ray LaHood declared that air travel was safe and there was no reason to cancel flights.

Kelly, the CEO of Dallas-based Southwest, said air travel is safe but that his airline had instructed employees to be vigilant about washing hands, sanitizing aircraft and looking out for fellow workers or passengers who appeared ill.

Anyone who looks ill will be given a paper mask to wear during the flight, he said.

Alaska Airlines said it was removing pillows and blankets from all of its 114 planes, and would disinfect and sanitize all of its planes during overnight maintenance. It said crews were also doing an extra interior cleaning of planes arriving from Mexico in between flights.

Sabre, a major airline reservation and ticket-distribution company, said other than a decline in trips to Mexico, travel within the United States and to other parts of the world appeared to be holding steady.