Supervalu (SVU) disclosed a deeper fiscal third-quarter loss and cut its guidance on Wednesday as the grocery-store chain was hit by weaker-than-expected sales.

In the wake of the quarterly results and new guidance, shares of Minneapolis-based Supervalu plunged more than 10% in premarket trading.

The No. 3 U.S. supermarket chain said it lost $750 million, or $3.54 a share, last quarter, compared with a loss of $202 million, or 95 cents a share, a year earlier. Excluding one-time items, it earned 24 cents a share, matching expectations from analysts.

However, net sales slumped 4% to $8.33 billion, missing the Street’s view of $8.42 billion. Same-store sales dropped 2.9%.

Supervalu alarmed shareholders by downgrading its sales guidance, now projecting full-year revenue of about $36.1 billion, compared with forecasts from analysts for $36.5 billion. The company maintained its view for 2012 non-GAAP EPS of $1.20 to $1.30, which is in-line with estimates.

Same-store sales are expected to decline between 2.5% and 3%, excluding fuel.

“Even with the ongoing difficult economic environment and pressured consumer, we continued to make progress against our plan, allowing us to invest in price to deliver everyday value and hyper local choices that meet the needs of our customers in the diverse neighborhoods we serve,” CEO Craig Herkert said in a statement.

Supervalu’s stock, which has rallied almost 11% over the past year, tumbled 9.42% to $7.60 ahead of the open.

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