NEW YORK (AFP) - American Airlines said on Tuesday it had grounded all its aircraft due to problems with its reservation system.

"American's network system is experiencing intermittent outages," AA said.

"We are on a system-wide ground delay that will last until 4pm CST (5am, Singapore time) as we work to resolve this issue as quickly as we can," the company said, apologising to customers for "any inconvenience."

In a Twitter message, AA said: "The issue is w/ our ability to access our res system & not w/@SabreNews. We apologise to Sabre & customers for confusion.

In an earlier tweet, AA had said the Sabre reservation and booking tool was offline.

The number of flights held on the ground and passengers affected were not immediately available.

American said there would be no charge to customers wanting to change their reservations and the airline would provide "full refunds" if their travel plans were not flexible.

"However, we are unable to make changes to current travel plans until we have resolved this issue." American, whose parent AMR Corporation is struggling to emerge from bankruptcy, plans to merge with US Airways to create the largest US airline.

It would also help lift AMR from bankruptcy reorganisation, where it has been since November 2011.

The deal won US bankruptcy court approval in mid-February. Following other approvals required, the merger is expected to be completed by the third quarter of 2013.

The combined airline, to keep the American Airlines name, is to be led by current US Airways chief executive Doug Parker.