Amazon.com Inc (AMZN.O) on Wednesday unveiled more discounts on several grocery products at Whole Foods Market (WFM.O), days ahead of the U.S. Thanksgiving holiday, sending stocks of rival U.S. grocers lower in early trading.

The lower prices include deeper discounts on some items for Amazon Prime members and come on top of price cuts already announced by Whole Foods in August, when Amazon completed its US$13.7 billion acquisition of the upscale grocer.

Shares of rival U.S. grocers including Costco (COST.O), Sprouts Farmers Market (SFM.O) and Kroger (KR.N) all fell on Wednesday morning following the announcement.

Investors have closely followed any signals of price cuts at Whole Foods for its effects on the U.S. grocery industry, which is already reeling under a brutal price war.

Amazon, which forayed into brick-and-mortar retailing with its purchase of Whole Foods, could upend the grocery industry and undercut traditional retailers by using its deep pockets and large presence, analysts have said.

Whole Foods said it would sell organic turkey for US$3.49 per pound to all customers, while Prime members could buy it at an even lower price of US$2.99 a pound.

It will also offer lower prices on items from national brands including Chobani Yogurt and Applegate Hot Dogs as well as smaller organic brands such as Eden Foods.

"These are the latest new lower prices in our ongoing integration and innovation with Amazon, and we're just getting started," Whole Foods CEO John Mackey said in a statement.

A study last month showed Whole Foods' previous price cuts on items including bananas, avocados and beef had drawn customers away from retailers such as Wal-Mart, Trader Joe's and Sprouts Farmers.