The ratings agency Fitch on Friday downgraded Belgium's longterm debt rating one notch to AA-, citing growing levels of sovereign debt, but said the European nation's outlook was stable.

Belgian efforts to stimulate growth through structural reforms since a new government took power in 2014 have pushed the country's fiscal targets upward, with gross debt forecast to be 107 percent of GDP in 2016, the agency said in a statement.

"This persistent fiscal slippage moves back the first year with substantial debt reduction to 2019, two years later than previously projected by Fitch in November 2014, when the agency placed Belgium's rating on negative outlook," the statement said.

With tax revenues falling, the agency is now forecasting a three percent deficit for the Belgian budget in 2016, up three tenths from a prior estimate.

Extraordinary costs associated with the refugee crisis as well as security measures in response to terrorist attacks in France and Belgium also pushed the deficit forecast higher by 0.2 percent of GDP, according to Fitch.

"Repeated slippage against government targets is negatively affecting fiscal policy credibility, and reduces confidence in the ability to meet future fiscal targets."