TAIPEI ? A leading Taiwan flat-screen maker said Sunday its three top executives had been barred from leaving the United States for their alleged role in a price-fixing case.

AU Optronics vice-chairman H.B. Chen, president Chen Lai-juh and board member Hui Hsiung flew to the United States last month to attend a pre-trial hearing but have since been banned from leaving.

The company said it was not clear when they would be allowed to depart, but spokeswoman Hsiao Yawen said "the company has hired lawyers to help resolve the case".

"But the company has made it clear we'd like to cooperate with the US authorities in the investigation of the case, and they would fly back to the US whenever needed," Hsiao said.

The decision not to allow them to leave may have been taken because there is no extradition treaty between Taiwan and the United States, local media said.

A federal grand jury in San Francisco in June charged the three and three others with conspiring to fix LCD prices between September 2001 and December 2006.

AUO has denied the charges and pleaded not guilty.

Two former executives with Taiwan's Chunghwa Picture Tubes Ltd and one from South Korea's LG Display Co Ltd have already been indicted in the same case, part of a sweeping US probe into price-fixing worldwide.

The executives face a maximum of 10 years in prison if convicted and fines of one million dollars each.

Six electronics firms have pleaded guilty in connection with the case and paid fines totalling more than 860 million dollars. Seventeen executives have been charged so far.