Standard & Poor's raised Greece's credit rating to low-speculative grade on Wednesday, lifting it out of default territory as expected, after Athens completed the biggest sovereign debt restructuring in financial history.

"While the exchange has, in our view, alleviated near-term funding pressures, Greece's sovereign debt burden remains high," S&P warned as it raised the credit rating to CCC, with a stable outlook.

The rating firm warned that the recession and a May 6 general election were posing risks to fiscal adjustments needed to further cut Greece's debt.

"The ratings could be lowered if we believe that there is a likelihood of a distressed exchange on Greece's remaining stock of commercial debt," it said in a statement.

Fitch assigned Greece a speculative B-rating mid-March, becoming the first major rating agency to lift the country out of default territory after the debt swap cut Athens' debt mountain by about 100 billion euros, or close to a third.