"Although the immediate market volatility has subsided, the policy uncertainty and the ultimate financial and political spillovers may last for months or years, leaving markets vulnerable to further confidence shocks," it wrote in a quarterly review of markets, Reuters wrote

Primarily, negotiations will stretch on for years, and the results may have far-reaching legal and economic implications for the United Kingdom's financial industry, as well as for foreign investment in the country, the report said.

U.S. regulators rely on the office, created by the Dodd-Frank Wall Street reform law, for research and risk analyses that will help them prevent another financial meltdown on the magnitude of the 2007-09 crisis.

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Read alsoBoris Johnson: Brexit does not mean leaving EuropeInvestors sought shelter from the market turmoil in bonds after Britain's referendum, sending long-term interest rates in the United States, the United Kingdom and Germany to historic lows, according to the report.

Meanwhile, global equities lost an estimated $3 trillion in market value in two days and a rebound in oil prices came to a halt.

Since then, volatile investments known as risk assets have rebounded sharply in the United States, and equities in Europe have recovered more than half their declines, according to the report.