Warren Buffett on Saturday lamented the lack of attractive investments available to his sprawling $713bn Berkshire Hathaway conglomerate, warning that low interest rates over the past two years had inflated valuations across financial markets.

The musings, in Buffett’s long-anticipated annual letter, accompanied results that showed Berkshire’s operating profits had soared 45 per cent from a year before to $7.3bn in the final three months of the year. The gains were propelled by strong results from its BNSF Railway and the string of electric utilities it owns.

Buffett, 91, told Berkshire investors that both he and his longtime right-hand man Charlie Munger had found “little that excites us” as they sought out investments with which to plough some of the group’s gargantuan $146.7bn cash pile into.