A credit downgrade that pushed Spain to within a whisker of 'junk' rating unnerved investors and forced Italy to pay a slightly higher yield at a bond auction on Thursday.

Rome's borrowing costs on the three-year bond rose to 2.86 percent from 2.75 percent at a similar sale one month ago, halting a downtrend started at the beginning of summer.

However yields over three-year Italian debt has sunk from peaks of around 5.3 percent in June and Rome has already covered 80 percent of its borrowing needs.

Italy sold on Thursday its maximum targeted amount of 3.75 billion euros for the issue. Results for the off-the-run bonds are due later.

(Reporting by Francesca Landini)