Shares in Germany's Commerzbank fell to their lowest level for more than two decades because of fears about its finances.

I wouldn't say we're being treated differently by other banks

Rudi Duttweiler Commerzbank treasurer

The sell-off came after the credit rating agency Standard & Poor's cut the company's credit ratings and warned about further problems from the bank's weakening shareholdings.

Germany's third-largest listed bank fell more than 7% percent to 5.04 euros after S&P said that the fall in the value of Commerzbank's equity reserves would weaken its financial flexibility.

At the same time, there were signals that rival banks were beginning to grow cautious about doing business with Commerzbank and other German banks, particularly in the complex field of credit derivatives.

But a Commerzbank spokesman said that the bank's relations to other derivatives traders remained normal. "There is not a disturbance in this market," he said.

Business as usual

In the key inter-bank lending market, where banks rely on overnight loans from one another, Commerzbank treasurer Rudi Duttweiler told Reuters news agency that business was continuing as normal.

"I wouldn't say we're being treated differently by other banks.

"I don't see us being treated differently on the money market side," he added.

Commerzbank has repeatedly denied facing solvency problems but it has lost more than 71% of its stock market value in the past six months.

Concern about Commerzbank's operating performance has been heightened in recent weeks by the rising cost of bad loans, the slump in its equity portfolio and talk of big trading losses.

"The current slide in German banking stocks is certainly exaggerated, but at the same time Germany is a very difficult terrain for banks," said Andreas Schaefer, a fund manager at Activest in Munich.