Egypt ? Al-Qaida-led Iraqi insurgents issued a video Thursday purporting to show the killing of 20 kidnapped Iraqi police and soldiers, 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 including al-Qaida 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 northern 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.