“It’s unfortunate there’s no way to stop it,” Mr. Terry said, even though “this is what these guys are over there fighting for: freedom of speech.”

One YouTube user, who would not identify himself other than by his account name, facez0fdeath, and his location, in Britain, said by e-mail that he posted a video of a sniper attack “because I felt it was information the U.K. news was unwilling to tell.”

“I was physically sickened upon seeing it,” he said, adding, “I am wholly opposed to any form of censorship.”

The video he posted, which had been viewed more than 33,000 times, was removed earlier this week.

Another YouTube user, who said he was a 19-year-old in Istanbul and who posted more than 40 videos of Iraq violence, said via e-mail that “anti-war feelings and Muslim beliefs (the religion of peace) motivates me.”

Neal O. Newbill, a freshman at the University of Memphis who viewed some of the YouTube videos and posted comments on them, said in an interview that he was enraged by the recorded chants of “Allahu Akbar,” Arabic for “God is great,” that follow some of the sniper attacks.

But Mr. Newbill added that he was awed by the size of the blasts from the improvised explosive devices, or I.E.D.’s, used against American vehicles. A son, nephew and grandson of American veterans, Mr. Newbill said he had sought out the videos, searching on YouTube for “I.E.D.,” “because I like watching stuff blow up.”

The Web sites also contain a growing number of video clips taken by American soldiers. One shows the view from the back of a truck containing several members of a platoon, whose vehicle then hits an I.E.D. and is turned on its side. A few videos also show American servicemen or private security guards firing at attackers, and one shows an American rocket-propelled grenade hitting a building from which insurgents are firing.