FRANKFURT (Reuters) - RWE shares extended losses on Wednesday after the group's management failed to dispel investor concerns about a report that the company could buy into a U.S. operator of gas-fired power plants.

Earlier this month, magazine PeakLoad reported that RWE was in advanced talks to buy a minority stake in U.S. power plant operator Calpine, causing RWE shares to fall by 7% over concerns about RWE's capital allocation and whether such a deal would fit within the group's green strategy.

RWE CEO Markus Krebber on Wednesday declined to comment on the report during an analyst call discussing first-half results, only saying RWE had no integrated set-up in the United States that covers flexible generation, a term the company uses for gas capacity.

But Krebber said RWE saw merit in such a set-up in the United States, adding it would carefully approach reviewing potential opportunities and that nothing would happen "overnight".

Shares in RWE were down 3.4% at 1203 GMT, at the bottom of Frankfurt's blue-chip index.