An Al Qaeda-linked insurgent group posted a Web video Friday showing what it said was the downing of a U.S. military helicopter earlier this week. Seven Americans were killed in the crash.

The U.S. Marines commandant Gen. James Conway has said the Marines do not believe that the CH-46 Sea Knight helicopter was shot down in the crash Wednesday northwest of Baghdad. U.S. military officials said early indications were that the craft's loss was due to mechanical failure.

Click here to view the video at SITEInstitute.org

The two-minute video -- which says it shows the "downing of U.S. aircraft on Feb. 7" -- shows a helicopter that appears to be a Sea Knight flying. At least one object trailing smoke is seen in the sky nearby, and then the craft bursts into orange and red flames, with a spray of debris emerging from it.

It is not clear whether the object is a rocket, and it cannot be clearly seen connecting with the craft.

In the footage, the helicopter heads downward, but appears to be at least partially in control, though smoke and bright flames are trailing from it and growing in size. The helicopter then disappears behind a line of trees as it hits the ground.

The video was issued by the Islamic State in Iraq, an umbrella group of Iraqi insurgent groups that includes Al Qaeda in Iraq. The group on Wednesday issued a written claim of responsibility for the craft's downing and had promised a video would follow.

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The video, titled "the Hell of Christians and Apostates in Iraq," was posted on a Web forum where the group and other Islamic militants often post messages. Its authenticity could not be independently confirmed.

The video, as did Wednesday's written statement, identifies the downed helicopter as a Chinook. The Marines' Ch-46 Sea Knight resembles the Army's Chinook transport helicopter in that both have double rotors -- though the Sea Knight is smaller.

The craft in the video has features of the Sea Knight: three landing gear and "sponsons" -- or fin-like appendages -- near the back. The Chinook has four landing gear and no sponsons.

As the footage is shown, the video plays an old speech by Al Qaeda leader Usama bin Laden, urging fighters, "Do not seek permission from anyone in the killing of the Americans. Go ahead with God blessings."

It also plays a mujahedeen (holy warriors) song, with lyrics, "Burn the Christians, fight the devious Christians who worship crosses."

Wednesday's crash was the sixth by a U.S. helicopter since Jan. 20 -- at least four of them downed by ground fire. An Iraqi air force officer on Wednesday said the CH-46 had also been shot down. Five Marines and two Navy medics were killed in the crash.

Though he said the CH-46 was not believed to have been shot down, Conway said Wednesday there was a new and troubling "intensity of effort" by insurgents to attack helicopters.

The most commonly seen anti-aircraft missiles among insurgents is the SA-7, which Marine troop transports have equipment to avoid, Conway said.

But he said more modern, portable anti-aircraft missiles, the SA-16 and SA-18 had behun to appear. The SA-16 uses a more advanced infrared guidance system and is effective at altitudes of up to about 10,000 feet.

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