A video purportedly showing an attack against British troops last week was posted Sunday on an Islamic Web site.

Soldiers from Britain's Black Watch (search) regiment were manning a vehicle checkpoint south of Baghdad (search) when a bomber blew up his vehicle and other insurgents fired mortars at the position on Thursday, killing three soldiers and wounding eight more, according to British officials.

Al Qaeda-linked followers of Jordanian militant Abu Musab al-Zarqawi (search) had earlier claimed responsibility for the attack.

A subtitle on the videotape claimed "The first martyrdom operation against the British forces in Baghdad" before a car was shown slowly driving down a road before it bursts into flames.

The video later shows a blown-off arm and a person, partially off-camera, kicks the arm around before he forcefully steps on it. A subtitle reads "these are some of the body parts that they have not seen because there were so many."

Off-camera, a voice yells out "Allahu Akar," or "God is Great." The tape also shows military vehicles and a helicopter hovering nearby.

At one point, a voice proclaims: "I swear...that the head of America has been rolled in the dust and trampled on by our heroes."

A spokesman for the British Ministry of Defense said officials were unable to authenticate the video.

"It does however appear to show an attack against coalition forces," he said on condition of anonymity.

The British forces had been sent from relatively peaceful southern Iraq to the high-risk area near Baghdad to free up U.S. forces for an assault on the militant stronghold of Fallujah.

The three deaths represented the worst combat loss suffered by British troops since Aug. 23, 2003, when three Royal Military Police were killed in southern Iraq. So far, 73 British troops have been killed.

An Iraqi interpreter also killed, British officials said.

Al-Zarqawi's group, formerly known as Tawhid and Jihad, is believed responsible for numerous car bombings and beheadings of foreign hostages.