PRAGUE (Reuters) - The Czech Republic has launched a tender for frequencies for next-generation 5G networks, its telecoms regulator CTU said on Friday, sparking criticism from potential bidders.

The auction of frequencies in the 700 MHz and 3.4-3.5 GHz bands is aimed at boosting competition in a market where high prices have long been a gripe of customers and politicians.

Interested bidders have until Sept. 30 to apply, CTU said.

The regulator said that after public consultations it had reserved a section of 2x10 MHz in the 700 MHz band for new entrants.

CTU also set spectral limits in both bands and said existing operators would need to provide national roaming services for newcomers should they succeed in the auction.

O2 Czech Republic <SPTT.PR>, Deutsche Telekom's T-Mobile and Vodafone <VOD.L> are the country's existing operators.

The latter said that the auction was not well prepared.

"Given the mistakes and problems in the conditions, it can be expected that the auction will result in clashes at courts and also the European Commission," Vodafone said in a statement.

T-Mobile said it was surprised by the CTU's action.

"We have to study the conditions and ponder our next steps, including possible charges," spokesman Jiri Janecek said.

Last month, O2 Czech Republic complained to the European Commission over some 5G auction conditions.

The planned auction for new 5G frequencies has been hit by delays as the state seeks to attract a fourth operator.

In January, the former head of CTU resigned over government changes to the auction, saying they risked slowing the rollout of the technology and were likely to result in court disputes.

(Reporting by Robert Muller and Jason Hovet; Editing by Kirsten Donovan and Louise Heavens)