SAN FRANCISCO (Reuters) - Amazon.com Inc will release a set-top TV box later this year that will stream video over the Internet, challenging Apple Inc's Apple TV device and a similar gadget sold by start-up Roku, BloombergBusinessweek reported on Wednesday.

The box will plug into TVs and give viewers access to Amazon's digital video content, which the company has been expanding, BloombergBusinessweek said, citing three unidentified people familiar with the project.

An Amazon spokesman did not immediately respond to a request for comment.

Amazon's video content is already available on other set-top devices, including Roku. Building its own gadget will help Amazon put the content more directly in front of consumers and give developers another reason to create apps for Amazon's digital platform, BloombergBusinessweek said.

The set-top box is being developed by Amazon's Lab126 division, based in Cupertino, California, near Apple's headquarters. It's being run by Malachy Moynihan, a former vice president of emerging video products at Cisco Systems Inc, BloombergBusinessweek added.

(Reporting by Alistair Barr; Editing by Carol Bishopric)