Shares in IKB Deutsche Industriebank fell more than 20% in Frankfurt this morning on concerns the troubled German lender will need a further €2bn ($2.9bn) from its investors to cover losses stemming from its US sub-prime mortgage exposure.

IKB, which was the first bank casualty of the mortgage crisis that erupted at the end of July last year, secured a rescue package worth more than €6bn last year, but the further decline in sub-prime mortgage markets since then means it may need to call on its investors for more guarantees, according to German Sunday newspaper Frankfurter Allgemeine Sonntagszeitung.