American Airlines said its reservation system had an outage on Tuesday, leading to a system wide delay that grounded the carrier's fleet and halted its flights at least through late in the afternoon.
The company said it grounded flights until 4 p.m. CDT (1700 EDT) as it tries to resolve the problem. American, a unit of AMR Corp, operates more than 3,500 daily flights worldwide.
Earlier, The Wall Street Journal said federal regulators had grounded the carrier's flights following the outage. The Federal Aviation Administration did not immediately respond for comment.
The move affects potentially hundreds of flights across the United States. It was not immediately clear when the problem would be resolved.
Other carriers have also had problems with system outages. Last year, computer outages at United Continental Holdings stranded passengers at airports around the country.
American plans to merge with rival US Airways Group to form the world's biggest air carrier.