Italy sold the top planned amount of 5 billion euros at a bond auction on Thursday, meeting sound demand ahead of a crucial sale of five- and 10-year paper on Monday.

At the first auction held after a two-notch sovereign downgrade by Standard & Poor's, yields on two-year, zero-coupon bonds fell to 3.76 percent compared with an auction level of 4.85 percent at the end of December.

It was the lowest yield since August 2011.

Italy sold 4.5 billion euros of the new January 2014 CTZ bond, at the top of its planned range.

On Thursday, Italy also sold 500 million euros of an off-the-run September 2014 BTPei last auctioned in 2005.

(Reporting by Valentina Za)