Italian bonds came under pressure on the money markets on Wednesday when the Treasury failed to hit its target in an auction of five-year and 10-year bonds.
The Treasury sold a total of 5.74 billion euros of bonds, compared to a target of 6.25 billion, and had to offer higher yields.
The yield on 10-year bonds went up to 6.03% from 5.84% at the last equivalent auction in April and it climbed to 5.66% from 4.86% on the five-year ones.
Yields of 7% or higher are generally considered unsustainable in the long run, given that Italy has a massive national debt of around 120% of GDP.
After the auction, the yield spread between 10-year Italian bonds and the German benchmark, a key indicator of market confidence in Italy's ability to weather the eurozone crisis, went beyond the 470-point mark for the first time since January 17.
The spread, which closed at 438 points on Tuesday, has been climbing in recent weeks amid concern about Greece's future in the eurozone.