Fitch Ratings has affirmed the long-term ratings of Australia's four major banking groups - ANZ, Commonwealth Bank, National Australia Bank and Westpac - at AA-.Cautionary factors noted by Fitch include a warning that the four banks' "reliance on wholesale funding is high relative to international peers."Fitch said it "expects the banks to focus on improving funding stability - either through further lengthening of wholesale funding and/or increased use of customer deposits", an approach that is contrary to the recently stated preference of Commonwealth Bank, at least, taking into account the easing of funding costs in wholesale markets.Fitch said it expected revenue growth "to come under some pressure during 2013 as a result of modest credit growth and continued elevated funding costs, particularly for deposits."The ratings agency also said it "expects a mild deterioration in the operating environment in Australia, which may place some modest pressure on asset quality and result in impairment charges."Fitch said the banks' capital positions were "adequate for their business mix and risks", and said the four banks will have little difficulty meeting the Basel III capital requirements.Fitch said the rating upside for the major Australian banks was "limited, given their current high ratings and weaker funding profile relative to those of similarly rated international peers."The ratings agency said ANZ and NAB faced greater risks than CBA and Westpac because of their offshore investments.