Telenor concerned about Vimpelcom operations: CEO

OSLO, July 24 (Reuters) - Norwegian telecoms firm Telenor is concerned about the operational performance of Russia's Vimpelcom and is working with the firm to produce improvements, Chief Executive Jon Fredrik Baksaas told a news conference on Tuesday.

Telenor boosted its voting stake in Vimpelcom to 36.36 percent in mid-February, although the increase has been challenged by Russian anti-monopoly authorities.