Moody's downgraded Italy's ratings to A2 from Aa2, a lower rating than that of Estonia, and kept a negative outlook on the rating, a sign that further downgrades are possible within the next few years.

The move comes after Standard and Poor's cut its rating on Italy to A/A-1 from A+/A-1+ on September 19 and underlines growing investor uncertainty about the euro zone's third largest economy, which is now firmly at the center of the debt crisis.

"The negative outlook reflects ongoing economic and financial risks in Italy and in the euro area," Moody's said in a statement.

"The uncertain market environment and the risk of further deterioration in investor sentiment could constrain the country's access to the public debt markets," it said.