(Adds details on forecast, updates share price)
Sept 8 (Reuters) - Kroger Co forecast comparable-store sales below Wall Street estimates on Friday and said it would stop giving longer-term forecast, sending shares of the biggest U.S. supermarket company down 6 percent.
The weak forecast came as Kroger, which operates some 2,800 stores across the United States, reported a fall in second-quarter earnings as it discounted heavily to fend off competition from Wal-Mart Stores Inc and other retailers.
Kroger said it expects sales at stores for at least a year to rise 0.5 percent to 1 percent, excluding fuel, for the remainder of the year.
Analysts on average were expecting a 1.2 percent increase in comparable-store sales in the third quarter and 1.7 percent in the fourth quarter, according to Consensus Metrix.
Kroger said it would no longer provide longer-term forecasts, given what it called a "dynamic operating environment."
U.S. retailers have struggled in the face of intensifying competition from Amazon.com Inc as more people shop online.
Amazon's purchase of upscale grocer Whole Foods Market has added to concerns that retailers would be forced to cut prices more aggressively to hold on to customers.
Amazon last month lowered prices on Whole Foods items such as avocados, bananas and beef, contributing to price declines ranging from just over 1 percent to as much as 9 percent, according to analysts.
Kroger has also slashed prices, in particular on staples such milk and eggs, analysts have said.
Kroger's net earnings fell 7.8 percent to $353 million or 39 cents per share in the second quarter ended August 12, matching analysts' average expectation on a per-share basis, according to Thomson Reuters I/B/E/S.
Excluding fuel, sales at Kroger stores open for at least a year rose 0.7 percent in the quarter, beating analysts' estimates of a 0.4 percent increase, according to Consensus Metrix.
Sales climbed 3.9 percent to $27.60 billion, edging past analysts' estimates of $27.49 billion.
Kroger's shares fell 6.7 percent at $21.25 in early trading. The stock has fallen about 25 percent since mid-June as Kroger cut its yearly earnings forecast and following Amazon's announcement of its deal to buy Whole Foods. (Reporting by Vibhuti Sharma in Bengaluru; Editing by Sai Sachin Ravikumar)