WASHINGTON — U.S. intelligence officials have concluded that terrorist leader Abu Musab al-Zarqawi was the person shown on a video beheading an American civilian in Iraq, based on an analysis of the voice on the video, a CIA official said Thursday.

Intelligence officials conducted a technical analysis of the video released on an Islamic web site May 11 and determined "with high probability" that the person shown speaking on the tape — wearing a head scarf and a ski mask — is al-Zarqawi, a CIA official said, speaking on the condition of anonymity.

The person who is shown speaking in the video — determined to be al-Zarqawi — is then shown on the video decapitating American citizen Nicholas Berg, the official said.

Berg's body was found in Baghdad on Saturday. On Tuesday, an Islamic Web site released the video, titled "Sheikh Abu Musab al-Zarqawi slaughters an American infidel with his own hands."

The speaker on the video, now believed to be al-Zarqawi, reads a lengthy statement criticizing Islamic scholars and taunting the crusaders.

Standing alongside four other militants wearing headscarves and masks to disguise themselves, al-Zarqawi then kills Berg.

Al-Zarqawi is thought to be in Iraq, operating his own terrorist network, known simply as the "Zarqawi network." A specialist in poisons, he is thought to have extensive ties across the militant Islamic movement and is considered an ally of Osama bin Laden.

As recently as March, U.S. officials said al-Zarqawi's practice was not to make taped public pronouncements or take credit for attacks. However, in the last five weeks, he has increased his public profile with at least three recordings, including Berg's beheading.

Al-Zarqawi is believed to be behind well over a dozen high-profile attacks in Iraq, and many other acts of violence, which have killed hundreds.

The United States is offering a $10 million reward for information leading to his death or capture.