The moon is partly covered by clouds as it rises above the skyline of Frankfurt, Germany, early evening November 14, 2016. REUTERS/Kai Pfaffenbach

FRANKFURT (Reuters) - Several U.S. investment banks are scouting the market for available Frankfurt office space to shift parts of their business from London, the real estate executive of a large German bank said on Thursday.

Several concrete requests for vacant office space have been logged, Juergen Fenk real estate executive at German lender Helaba said at the bank’s annual press conference.

The European Central Bank expects London-based banks to seek ways to retain access to the European Union’s single market after Britain leaves the common trading bloc, the ECB’s top supervisor said on Thursday.

Hubertus Vaeth, who heads lobby group Frankfurt Main Finance, last month said he was confident that of the five leading U.S. investment banks, three will move some operations to Germany next year.

According to financial sources in Frankfurt, Citi C.N, Goldman Sachs GS.N and Morgan Stanley MS.N are on the lookout for office space in Germany's financial center.