Standard & Poor's downgraded Greece's credit rating by three notches Monday, making it the world's lowest after the agency said a likely debt restructuring would be considered a DEFAULT.

A restructuring of Greece's debt — either with a bond swap or by extending maturities on existing bonds — looks increasingly likely to be imposed by European policymakers as a means of sharing the burden of Greece's crisis with the private sector, S&P said in a statement.

"In our view, any such transactions would likely be on terms less favorable than the debt being refinanced, which we, in turn, would view as a de facto default according to Standard & Poor's published criteria," the agency said.

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