NATO authorities are dismissing an al Qaeda video that purportedly shows an insurgent offensive on U.S. and Afghan forces in southern Afghanistan.

NATO officers say they've checked their records and can find no engagements that would match the time frame claimed in the video.

Capt. Andre Salloum, a spokesman for the International Security Assistance Force, told The Canadian Press that no such attack had occurred within the region.

"I can tell you there has not been an extremist attack against an ISAF base within Regional Command South,'' said Salloum, a Canadian army spokesman attached to NATO in Kandahar.

"ISAF is committed to the government of Afghanistan and one video, or two videos, or three videos is not going to deter our commitment to rid this country of Taliban extremists.''

The tape begins with the deputy leader of al Qaeda, Ayman al-Zawahri, ridiculing U.S. President George Bush, in what appears to be an attempt to undermine American claims it is winning the war against the Taliban.

Al-Zawahri says Bush's claim to have deprived al-Qaeda of a save haven in Afghanistan is a "barefaced lie."

Al-Zawahri, who speaks in Arabic with an English translation in subtitles, appears to be referring to a speech Bush made in January when the president said that American troops "took away al Qaeda's safe haven in Afghanistan -- and we will not allow them to re-establish it in Iraq."

The video then goes on to show what it claims is an attack on a military position in Arghandab, in Zabul province some 160 kilometres northeast of Kandahar city.

The location falls under NATO's southern command.

The narrator, who sounds like the American al Qaeda member Adam Gadahn, claims that the position is "liberated" by the insurgents.

However, the film does not show the insurgents capturing the target during the night-time battle.

The video also shows the insurgents firing at the alleged post but it is impossible to identify the weapons in the dark.

It only shows the insurgents walking through the compound -- comprising mud-plastered buildings in a valley -- in daylight.

The night-time footage also shows tracer bullets crossing the sky, gunfire being exchanged and explosions of what are said to be rocket-propelled grenades.

"After a fierce battle, the mujahideen (holy warriors) begin their retreat from the zone of operations," the narrator says in English.

The tape quotes a fighter as saying: "We retreated after about 45 minutes of fighting."

Scrawled on the walls of the single-story buildings once occupied by American soldiers 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.

The authenticity of the scenes shown could not be confirmed.

The English-speaking narrator says the camera is going around "the liberated area to bring us pictures from inside the cleansed military bases."

The video also shows a crowd of men stoning a beige pickup truck that has the number RTS323 on its hood.

The narrator says: "The mujahideen and local residents celebrate the victory in their own special way."

The vide, which carried the logo of the al Qaeda media production company, as-Sahab, was posted on an Islamic website known for hosting extremist material.

Al Qaeda appears to have issued the tape on Thursday with the title "Holocaust of the Americans in the land of Khorasan, the Islamic emirate: Capture of an American post, Arghandab." The name Khorasan refers to Afghanistan.

The video raises some interesting questions about al Qaeda's operations, CTV's Tom Clark reported from Kandahar.

"In the past we were always told al Qaeda operated in the eastern part of Afghanistan. We're here in the south, but in the south it was always just the Taliban that the Canadians were fighting," Clark told CTV's Canada AM.

"That incident, if it's real, occurred just a little bit north of where I'm standing right now. The question that it raises is: Are we now fighting al Qaeda as well as the Taliban? We simply don't know at this point," Clark said.

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District chief of Arghandab, Fazel Bari, told The Associated Press the only recent clash in the area was last month when suspected Taliban militants ambushed NATO-led troops and Afghan forces on the road between Arghandab and Qalat, the provincial capital.

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

With files from The Associated Press and The Canadian Press