The default rate for commercial mortgages bundled and sold as bonds rose 0.42 percentage point to 4.71% last month, and may climb to 12% in 2012, according to Fitch Ratings.

Loans packaged from 2004 to 2008 account for more than 75% of total delinquencies, Fitch said Monday in a statement.

An increased number of loans exceeding $100 million were made in 2006 and 2007, when underwriting was most aggressive, and defaults on these mortgages will be a "significant contributor" to future delinquencies, Fitch said.

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