Amazon.com on Friday began letting gift-givers send Kindle electronic books by email as the leading online shop positioned itself to cash in on the year-end holiday season.

Kindle digital books can be read on computers, smartphones, iPads, and iPod touch devices as well as on the eponymous tablet sold by Amazon.

"We are thrilled to make it easier than ever for our customers to give their favorite Kindle book to a friend or family member as a gift," said Kindle vice president Russ Grandinetti.

"We're making this functionality available in time for the holidays to offer an easy, stress-free holiday shopping option for anyone -- not just Kindle owners."

The massive library of gift books available at amazon.com/givekindlebooks includes "The Girl Who Kicked the Hornet's Nest" and "The Immortal Life of Henrietta Lacks."

US spending on e-books was expected to total 966 million dollars this year, up from 301 million dollars last year, and to reach 2.81 billion dollars in 2015, according to a report this month by Forrester Research Inc.

Forrester said the number of e-book readers in the United States was expected to grow from 3.7 million at the end of last year to 10.3 million at the end of this year, hitting 29.4 million in 2015.

Seven percent of online US adults who read books read e-books, a number that is expected to double a year from now, Forrester said.

Forrester also said Amazon's Kindle store "stands to benefit tremendously" from the rise in e-book reading because of its existing relationship with book buyers through Amazon.com.