Al Qaeda-led Iraqi insurgents issued a video Thursday purporting to show the killing of 20 kidnapped Iraqi police and soldiers, each shot in the head execution-style as they knelt in a row.

The video showed a masked gunman walking down the row of captives, who were blindfolded with hands bound behind their backs outdoors in a clearing near trees. He shot them one by one, sending each tumbling forward as three other masked militants stood nearby, holding a black banner of the Islamic State of Iraq.

The Islamic State of Iraq, a coalition of Sunni insurgents incluiding Al Qaeda in Iraq, claimed on Saturday to have abducted the 20 and threatened to kill them after 48 hours unless the government freed female prisoners and handed over police accused of rapes in the norther town of Tal Afar.

The authenticity of the six-minute video could not be independently confirmed. It was posted on an Islamic militant Web forum where the Islamic State of Iraq has issued previous videos.

The Iraqi government has denied that 20 police and soldiers were kidnapped. Interior Ministry spokesman Brig. Gen. Abdul-Karim Khalaf said Thursday that the men in the video could not be identified and said the insurgents may have dressed up civilians to kill them.

"We checked with our commands then and all the troops were accounted for," Khalaf told The Associated Press. "They are immoral criminals. They have used all criminal methods and we don't rule out that they executed civilians who they dressed in military uniforms."

The video first showed the 20 men inside a room, lined up in three rows with black blindfolds over their eyes and their hands tied behind their backs. In front of a black Islamic State of Iraq flag, they wore blue police uniforms or military fatigues, and the camera focused on ID badges from the Defense or Interior Ministry on their chests. Some can be heard identifying themselves on the video and giving their positions in the military or security forces.

"I call upon the brothers in the national guards to agree to throw down their weapons and return to the path of God and Islam," said one after identifying himself as Mizher Jassem Mohammed Hussein, an engineer and army captain.

One of the men, wearing army fatigues, was seen shaking and swaying back and forth as he stood, then collapsing as his colleagues spoke.

The Islamic State of Iraq has claimed responsibility for attacks on Iraq's security forces, denouncing them as "apostates" helping U.S. troops, and has carried out numerous suicide bombings, most targeting Shiite civilians.