Frustrated U.S. travelers faced additional delays Saturday after a computer glitch grounded some flights and delayed others.

U.S.-based United Airlines said Saturday a problem with its computer network forced its airport processing and reservation to shut down, starting late Friday. Its website was also affected.

The company said it fixed the problem by early Saturday but that the resulting backlog could cause additional delays for another few days.

The computer system problems stranded thousands of passengers at major airports across the United States. Some were forced to spend the night at the airports or in hotels. Others rented cars to get to their destinations.

United Airlines said it was forced to cancel a total of 31 flights – 16 on Friday and another 15 on Saturday.

The company also said it would let passengers affected by the problem to book new flights at no extra charge.

Some United passengers expressed frustration with a lack of information from the airline about the problem.

United released a statement early Saturday on the Twitter micro-blogging site saying its systems were running again.

Several angry customers also used Twitter to convey their unhappiness with the airline.

United Airlines merged with Continental Airlines last year to form the world's largest airline group.