Standard & Poor's Ratings Services on Wednesday downgraded Greece's credit rating, voicing doubts that recent measures announced by the center-left government would be able to tame the country's ballooning public debt.

The downgrade came after another agency, Fitch, last week downgraded its own rating on Greece's national debt.

Standard & Poor's said in a statement it was cutting Greece's rating from A- to BBB+ with a negative outlook.