(Bloomberg) -- Complex debt trades that started as a way for lenders to reduce their loan exposure are becoming a business opportunity for some of the world's biggest investment banks. Others are worried they could become another source of systemic risk.

Nomura Holdings and Credit Suisse are among the most-active firms earning high fees by providing loans to help hedge funds buy so-called capital-relief bonds from other banks as investor demand for high-yielding securities increases, according to people familiar with the matter, who aren't authorized to talk about it and asked not to be identified. Those lenders are also facilitating trading, making it easier than ever for investors to buy and sell the instruments, the people said.

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