Standard & Poor's Tuesday downgraded a key measure of risk for Spain's banking sector, warning that the economic crisis will continue to have a negative impact on Spanish banks in the next 15-18 months.

S&P revised Spain's Banking Industry Country Risk Assessment to 4 from 3. The so-called BICRA scale ranges from Group 1, the strongest, to Group 10, the weakest.

Countries in the Group 4 include the Czech Republic, Israel, Korea, Mexico, and the Slovak Republic.