NEW YORK, March 11 (Reuters) - Italian businessman Diego Della Valle increased his stake in Saks Inc (SKS.N) with a series of stock purchases this week, strengthening his position as the second-largest investor in the U.S. upscale department store operator.

In three separate transactions between Monday 8 March and Wednesday 10 March, Della Valle bought a total of 2.9 million shares, raising his total to 11.4 million for a stake of 7.1 percent in Saks, according to a filing on Thursday 11 March with the U.S. Securities and Exchange Commission.

The last time he bought shares in Saks was last spring, when he raised his stake to 8.5 million shares, giving him 5.9 percent ownership as of May 5, 2009.

The three purchases this week cost Della Valle a total of $22.3 million.

Della Valle, the chief executive of Italian designer shoe and bag maker and Saks supplier Tod's SpA (TOD.MI), is Saks' largest investor after Mexican billionaire Carlos Slim, who owns 16.1 percent of the New York-based retailer.

Della Valle also owns the Fiorentina soccer club.

Saks shares were down 2 cents, or 0.3 percent, at $7.86 in early trading on the New York Stock Exchange. They have risen five-fold from lows hit a year ago this week. (Reporting by Phil Wahba, editing by Dave Zimmerman)