WASHINGTON (AP) -- Moody's (NYSE:MCO) Investors Service says Congress must go beyond its deal this week and come up with a plan to shrink the budget deficit if it wants to keep the U.S. government's top credit rating.

The credit rating agency says in a statement that it expects lawmakers in the coming months will take additional steps needed to lower the deficit, which has topped $1 trillion annually in each of the past four years. But if it fails to do so, the government's "Aaa" credit rating could be at risk.

Moody's had warned in September that it would likely cut its rating by one notch if the year-end budget negotiations failed. Moody's has a negative outlook on the government's debt, a warning of a possible downgrade.

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