Following a government meeting that updated the country's 2013 finance law and economic forecasts, Letta blamed the slippage on a "return to political instability".
Attempts by former prime minister Silvio Berlusconi to avoid being expelled from parliament following a tax fraud conviction have destabilized the government and sent the country's borrowing costs climbing.
Although the government wasn't in a position to set the public deficit under the EU ceiling in the revised budget, Letta said the objective is "within reach" and "does not require particularly significant measures" to achieve.
"We are keeping our promise to respect the 3.0 percent limit and all of our engagements to Europe," added Letta.
The EU only months ago removed Italy from the excessive deficit procedure, which entailed increased supervision and intervention from Brussels, as it had forecast Italy's deficit would come in at 2.9 percent in 2013.