BRUSSELS (Reuters) - EU antitrust regulators said on Thursday they were closing a preliminary investigation into Europe's biggest telecoms firms over development of new technology standards for mobile services.

The European Commission, which acts as competition watchdog for the 27-country European Union, said it was satisfied that the operators had handed standardization work over to the GSMA mobile industry grouping and other sector-wide associations.

It had been worried that work by five major operators - Vodafone, France Telecom, Telecom Italia, Deutsche Telekom and Telefonica -risked shutting out competitors and harming consumers.

"The Commission welcomes this transfer, which allows more stakeholder participation. It is a positive step that reduces the risk of standard setting work affecting competition negatively," the Commission said in a statement.

(Rex Merrifield, Brussels newsroom)