Citigroup poached the seven-year contract from its rival JPMorgan on the grounds that it is present in more markets, running its own proprietary custodian services in 62 different countries.
Citigroup said that Norges Bank Investment Management, which manages Norway's fund, needed a bank with more geographical spread as it seeks to diversify its investments beyond key developed markets in the US, Europe and Japan.
“For Norges to have a partner who is on the ground everywhere was essential, particularly in the new frontier markets,” Okan Pekin, global head of investor services at Citi, told the Financial Times newspaper.
Norges Bank Investment Management is one of the world’s largest investors, with an average stake of 1.3 per cent in every company listed on the world's stock exchanges.
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After a recent push to diversify, emerging markets now account for about 10 per cent of the bank's $530bn equity portfolio.