Kroger Co., the biggest U.S. supermarket operator, reported a better-than-expected quarterly profit, helped by its acquisition of grocer Harris Teeter earlier this year.

Shares of Kroger, which owns the Ralphs, Smith's and Food 4 Less chains, were up 4 percent at $49.25 in premarket trading.

Kroger said net income attributable to the company rose to $501 million, or 98 cents per share, in the first quarter ended May 24 from $481 million, or 92 cents per share, a year earlier.

Excluding items, the company earned $1.09 per share. Analysts on average had expected $1.05 per share, according to Thomson Reuters I/B/E/S.

Total sales increased 9.9 percent to $32.96 billion.