OSLO (Reuters) -The world economy appears to be fragmenting, posing the biggest risk to markets currently as it brings low growth and higher inflation, the CEO of Norway's $1.8 trillion sovereign wealth fund told Reuters. The fund, which invests the Norwegian state's revenues from oil and gas production, is the largest of its type and one of the world's biggest investors, owning on average 1.5% of all listed stocks and across some 9,000 companies globally. Asked what the biggest risk to financial markets today was, Nicolai Tangen, CEO of the fund's operator Norges Bank Investment Management (NBIM), said it was decoupling, and referred to one of the fund's stress-test scenarios that sees a fragmented world economy.