Washington (CNN) -- The U.S. military has blocked access to a range of popular commercial websites in order to free up bandwidth for use in Japan recovery efforts, according to an e-mail obtained by CNN and confirmed by a spokesman for U.S. Strategic Command.

The sites -- including YouTube, ESPN, Amazon, eBay and MTV -- were chosen not because of the content but because their popularity among users of military computers account for significant bandwidth, according to Strategic Command spokesman Rodney Ellison.

The block, instituted Monday, is intended "to make sure bandwidth was available in Japan for military operations" as the United States helps in the aftermath of last week's deadly earthquake and tsunami, Ellison explained.

U.S. Pacific Command made the request to free up the bandwidth. The sites, 13 in all, are blocked across the Department of Defense's .mil computer system.

"This is a response to a time of extreme demand for networks," Ellison said.

Ellison emphasized that it was a temporary measure.

"This blockage will be of a temporary nature and may increase or decrease in the size and scope as necessary," according to the message distributed to military announcing the move.

"We are doing this to facilitate the recovery efforts under way in Japan," Ellison explained. "We are trying to make sure we are giving them as many avenues and as much support as we can."

The blocked websites are:

* Youtube.com

* Googlevideo.com

* Amazon.com

* ESPN.go.com

* eBay.com

* Doubleclick.com

* Eyewonder.com

* Pandora.com

* streamtheworld.com

* Mtv.com

* Ifilm.com

* Myspace.com

* Metacafe.com