US retail giant Wal-Mart is to sue convenience store operator Kmart over use of its patented bag carousels.

Wal-Mart has a patent on the carousel that holds its plastic shopping bags. The cashier places items into bags and then spins the rack to make it easier for the customer to lift out the bags, reported Dow Jones News.

Wal-Mart filed a lawsuit in Delaware this week to prevent Kmart from using a similar device.

"The suit is a patent issue and that carousel device, as we have it, has been patented," Wal-Mart spokesman Tom Williams was quoted by Dow Jones International News as saying.

Williams said the carousels are used in more than 1,500 Wal-Mart stores, with more being added as new stores open and existing stores are remodelled.

Kmart spokesman Jack Ferry said the retailer has the carousels in fewer than 20 of its 1,512 stores.