Separately, Portugal's rating was reduced to "A-" from "A+," which is still considered investment grade.
The downgrades came after Greece last week announced it would finally tap a European Union-International Monetary Fund sponsored $53 billion bailout plan.
The news sent U.S. stock markets down sharply, as investor fears of a debt crisis contagion in Europe spread.
BUSINESS BRIEFS: Ingram Content Group works with Apple on iPadThe next Greek tragedy: default or bail-out?
