The regulation is intended primarily to prevent military Internet connections from being clogged with uploads or downloads of data-rich files such as video clips, said Defense Department spokesman Commander Jeffrey Gordon.

The ban is also meant to guard against infiltration by malicious or spying software hidden in files by hackers, according to Gordon.

"The bottom line is bandwidth; that is the most important thing," Gordon told AFP. "We have to make sure the network is reliable."

US soldiers in Iraq and Afghanistan have increasingly used community-oriented websites such as YouTube and MySpace to share videos, images or stories about their daily lives with loved ones and the world.

The regulation does not prevent soldiers from accessing the websites with their own computers and Internet connections.

However, most US soldiers deployed in battle zones in the Middle East are only able to access the Internet via Defense Department networks.

"It obviously impacts people deployed far greater than those in the US," Gordon said of the new rule. "Here you can just go home to your house and go online, or go to a coffee shop to get on the Internet."

US soldiers remain able to write online journals, or "milblogs," using DOD networks as long as they adhere to requirements not to reveal information that could jeopardize missions.

MySpace, YouTube and the other websites were targeted for restriction after a usage study showed they were the most visited websites by soldiers, according to Gordon.

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