WASHINGTON - The five-year spending plan outlined by the Pentagon earlier this year would cost $123 billion more than the US Defense Department projected and would violate budget limits set by Congress, the Congressional Budget Office said on Wednesday.

The CBO, in a 49-page analysis, said the main driver of growth in defense spending was the cost of operations and support, which accounted for 64 percent of the Pentagon's base budget in 2012. Pentagon plans would lead to significant rises in the cost of healthcare, salaries and operations and maintenance, it said.

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Pentagon officials declined to discuss the report. A spokeswoman said officials had not yet seen the document so it would be "premature for us to comment."

The analysis is likely to complicate efforts to resolve the divisive debate over the Pentagon's budget.