The Dutch competition authority raided the offices of mobile operators KPN, Vodafone, and Deutsche Telekom's T-mobile on Tuesday in a price-fixing investigation.

The competition authority, or NMA, said it was investigating whether mobile telecoms operators in the Netherlands engaged in cartel practices including price fixing and the sharing of market information.

It did not name any of the companies under investigation. However, KPN, Vodafone, and T-Mobile issued separate statements after the announcement saying NMA officials had been to their offices on Tuesday and that they were all fully co-operating with the authority's cartel probe.

KPN, the market leader, said its headquarters in The Hague were raided at 0830 on Tuesday morning, and that five employees were being questioned by the competition authority.

It said the competition authority was specifically investigating collaborative practices for consumer mobile telecommunications packages as well as KPN's sales channels.

T-Mobile spokesman Michael Vos told Reuters: We are co-operating fully with the authorities and we are confident of the positive outcome of the investigation.

Earlier, Dutch broadcaster NOS reported the investigation was prompted by two whistleblowers -- a former director at one of the companies and a board member at a telecoms firm.

A separate price-fixing case, which was launched in August 2001, recently found that the firms had engaged in a cartel in that year. KPN was fined 7.93 million euros, T-Mobile was fined 4.6 million euros and Vodafone was fined 3.72 million euros.

(Reporting by Roberta B. Cowan, Editing by Mark Potter)