Fitch ratings agency placed 12 major European and US banks on watch for possible downgrade on Thursday, citing their increased vulnerability to the heightened stresses on the global financial system.
Fitch downgraded two British, one Swiss and two German banks one notch each, after lowering its assumption that their respective governments would guarantee their survival in a crisis.
Among the 12 banks placed on negative watch were Barclays Bank, BNP Paribas, Credit Suisse, Deutsche Bank, Goldman Sachs, Morgan Stanley and Societe Generale, some of the world's largest banks, with substantial dependence on financial trading operations for income.
"The placement on Rating Watch Negative... reflects Fitch's view that these institutions' business models are particularly sensitive to the increased challenges the financial markets are facing," Fitch said in a statement.
"These actions are not tied to any specific earnings information as this review has been ongoing for some time," the ratings agency said.
"The review is motivated by Fitch's evolving concerns about aspects of these business models and the structural challenges they face, particularly during periods of market stress."
Fitch said its action served to highlight that the risks that remain in the markets are similar to the stress that banks and the global financial system felt during the 2008 crisis.
"Fitch recognizes that these institutions are diverse both in terms of product scope and geography and are among the largest in the world.
"However, recent history demonstrates that large banks can fail."
Fitch also cut the ratings on five banks by one notch each, after reassessing the commitment of their respective governments to assure their survival in a crisis.
The downgraded banks were: Germany's Landesbank Berlin and Berlin-Hannoversche Hypothekenbank, Switzerland's UBS, and Britain's Lloyds Banking Group and Royal Bank of Scotland.
The ratings firm explained that since the financial crisis in 2008, policymakers have moved to limit or preclude the use of taxpayer funds to rescue banks in a way that would protect their creditors.
While the creditor protection is still implicit in the eurozone as governments seek to maintain confidence during the ongoing Greek debt crisis, for the two British banks and UBS, Switzerland's biggest bank, which are outside the eurozone, the policy change has taken place, Fitch explained.
With the two German banks, the downgrade was mainly to bring their ratings in line with comparable banks.
"The tension is that this policy transition was primarily designed for the 'next crisis' while officials continue to grapple with the current one," Fitch noted.