The narrator on the English version of a video posted on the Web that Al Qaeda says shows an attack on U.S. and Afghan forces in Afghanistan is believed to be American Adam Gadahn, a member of Usama bin Laden's terror network who is on the FBI's most wanted list, experts said Friday.

Gadahn has appeared as a spokesperson under the name Azzam the American in previous Al Qaeda videos.

SITE Institute, which tracks terrorist groups, claimed the narration on the video — which is clearly an American accent — was done by Gadahn. U.S. intelligence officials said they believed it was Gadahn's voice, but were waiting for further analysis of the video.

Click here to view the video at SITEInstitute.org.

The video is an apparent attempt to disparage American claims of winning the war against terrorists in Afghanistan. Its release came as the United States and Britain plan to deploy more troops to the country after the worst year of insurgency-related violence since the Taliban regime was overthrown in 2001.

The 24-minute video carries the logo of the Al Qaeda media company, as-Sahab, and was posted on an Islamic Web site known for hosting extremist material. It was titled "Holocaust of the Americans in the land of Khorasan, the Islamic emirate: Capture of an American post, Arghandab." Khorasan refers to Afghanistan.

The tape begins with the deputy leader of Al Qaeda, Ayman al-Zawahiri, ridiculing President Bush's claim to have deprived Al Qaeda of a safe haven in Afghanistan as a "barefaced lie."

Al-Zawahri, who speaks in Arabic with an English translation in subtitles, seems to be referring to Bush's speech on Jan. 10 when the president said that U.S. forces "took away Al Qaeda's safe haven in Afghanistan — and we will not allow them to re-establish it in Iraq."

The version with the English narration shows video film of a purported attack on a military position in Arghandab, a district 100 miles northeast of the city of Kandahar.

The narrator claims that the position is "liberated" by the insurgents. The film does not show the insurgents capturing the target — a compound of mud-plastered buildings in a valley — during the nighttime battle. It only shows the insurgents walking through the compound in daylight.

"It is very likely that this base was voluntarily abandoned by coalition and Afghan forces, and that this (tape) is Al Qaeda trying to capitalize on a coalition tactical retreat," said Evan Kohlman, an analyst at the U.S.-based globalterroralert.com.

The authenticity of the scenes shown could not be verified. When asked about the video, the district chief of Arghandab, Fazel Bari, told The Associated Press that the only recent clash in that area was last month when suspected Taliban militants ambushed a NATO and Afghan force on the road between Arghandab and Qalat.

Bari said the NATO and Afghan troops suffered no casualties, but they detained one man after the battle, which ended with the Taliban retreating.

SITE Institute said the video, which it obtained Thursday, stood out out because of its length and the fairly high production values. The institute noted that it was distributed in two versions — Arabic with English subtitles and another with an English voiceover.

The footage shows what is said to be the mujahedeen reconnoitering the target, then firing. Tracer bullets cross the night sky, fire is returned and there are explosions of what are said to be rocket-propelled grenades.

"After a fierce battle, the mujahedeen begin their retreat from the zone of operations," the narrator says in English.

In the daytime footage, the video shows a dusty compound of single-story buildings which were once occupied by Americans soldiers. Scrawled on the walls are words such as: "Scalp Hunters," "CPT ASHWOKTH UTAH. N6 '06 ETT," and "Spc Smith Commo US Army 2006."

ETT stands for Embedded Training Teams — the U.S. and other Western soldiers who serve as mentors to the Afghan security forces.

An empty packet of Lay's potato chips is found. The camera focuses on the name of the Saudi manufacturer, Saudi Snack Food Co. Ltd., as the narrator says: "As is always the case in our tours of liberated bases, we find evidence that the primary financiers of this crusade are the puppet regimes of the Gulf."

An Afghan with a white beard and black turban tells the camera that local residents suffered under the foreign "devils."

"No one could leave his house, not even for absolutions and prayers. We couldn't even light a lamp at night ... The people are very happy about the coming of the Taliban," he says.

The video has an element of theater. It shows a U.S. helicopter flying overhead and a fighter trying to camouflage himself under dried grass. "The reconnaissance operation is not free of danger," the narrator says. But the fighter does not work with any urgency. He talks to the cameraman, who does not take cover himself.

FOXNews' Catherine Herridge and the Associated Press contributed to this report.