The new chief executive of Germany's flagship lender has conceded the bank faces an uphill battle against a barrage of bad "newsflow."

Deutsche Bank's long-running turmoil was dealt a fresh blow Thursday, when share prices tumbled after it was reported that the Federal Reserve labeled the bank's U.S. business as being in a "troubled condition."

Less than 24 hours later, influential group Standard & Poor's slashed its credit rating, potentially raising the cost of its borrowing. The ratings agency also questioned whether Deutsche Bank's CEO Christian Sewing would be able to return the bank to profit.

"Let's be straightforward: the newsflow is not good... I know that the current newsflow must give you the feeling that the bank is not getting any respite. That's why I think it's important for me to put this news in perspective," Sewing said in a letter to staff Friday.

"At group level, our financial strength is beyond doubt," he added.