(Adds Telenor, analyst, shares, detail)
OSLO, March 26 (Reuters) - The European Free Trade Association has opened antitrust proceedings against Norwegian telecom firm Telenor for allegedly infringing competition rules under the European Economic Area agreement, the trade body said on Wednesday.
EFTA's surveillance authority is investigating whether Telenor has charged prices resulting in an illegal margin squeeze on its competitors when offering retail mobile data services. The statement did not say which market the probe was focusing on, although it named Telenor's Norway subsidiary.
EFTA investigators raided Telenor's headquarters outside Oslo in December during which they collected "a significant amount of data", it said on Wednesday.
The investigation may be focusing on the Norwegian telecoms market, said an analyst.
"The statement may indicate that EFTA is looking into the way Telenor has packaged mobile data and whether it creates an anti-competitive effect because Tele 2 ... does not have the possibility to offer the same solutions based on wholesale conditions," said Espen Torgersen, an analyst at Carnegie, a brokerage based in Oslo.
Torgersen was referring to an agreement that Telenor has with competitors that they can rent capacity from Telenor's telecom network in areas in Norway where they do not have a network.
In those areas, Telenor customers were offered theoretical maximum download speeds that were faster than those from competitors renting from the network, according to a complaint made last year by Tele 2's Norwegian subsidiary, Network Norway.
Telenor denied it had infringed antitrust rules.
"We believe we have done nothing wrong in terms of competition regulation," said Telenor spokeswoman Torild Uribarri.
"The wording of their statement is quite general. We still don't have precise information about what this is about."
"The decision to open proceedings does not signify that the authority has made a finding of infringement or prejudge in any way the outcome of the investigation; it only means that the Authority will proceed with an in-depth investigation," EFTA said in the statement.
Shares in Telenor were up 2.1 percent at 1410 GMT, outperforming an Oslo benchmark index up 0.6 percent. Earlier in the day, Telenor announced it was selling a technology unit for 1.5 billion Norwegian crowns ($248.01 million), which analysts said had a positive impact on the stock. ($1 = 6.0480 Norwegian Krones) (Reporting by Joachim Dagenborg and Gwladys Fouche, editing by Louise Heavens)