American Airlines experienced significant computer system problems Tuesday, leading to hundreds of flight cancellations.

The carrier at one point was forced to initiate a system-wide ground delay for several hours, temporarily bringing its entire network to a halt and delaying thousands of passengers, as it worked to resolve problems with its reservation system. “Our systems have been fully restored,” the Dallas/Fort Worth-based carrier announced at 3:30 p.m. local time, but warned that delays and cancellations would occur through the remainder of the day as it recovered from the ground stop.

Earlier in the day, American had said on its Twitter feed that “the issue is with our ability to access our res system.”

According to the website, American canceled more than 425 flights and regional affiliate American Eagle canceled more than 330.