BAGHDAD -- Gunmen rounded up two Sunni families that had received death threats for joining US-organized talks with local Shi'ites, hauling away the men and boys and killing all six yesterday as suspected insurgents expanded a campaign of fear against opponents.
A recent wave of Sunni reprisals appears linked to increasingly high-profile attempts to stir popular momentum against Sunni extremists trying to drive out the Shi'ite-led government and its American backers.
Among those targeted include a range of Sunnis raising their voices against violence: imams, clan-based vigilantes, and activists trying to bridge deep rifts with majority Shi'ites.
"We are seeing more people beginning to challenge the insurgents," said Marine Brigadier General John Allen, who oversees units in the militant heartland west of Baghdad.
The two families gunned down at sunrise yesterday had received death threats for weeks after attending gatherings of Sunni and Shi'ite leaders, police said.
The first meeting, organized by US military officials on Feb. 13, brought together leaders of prominent clans from both sides, said military spokesman Major Webster M. Wright III.
The clan chiefs held another round on their own about a week later and appointed a joint council "to discuss the terms of reconciliation" around Youssifiyah, a Sunni-dominated area about 12 miles south of Baghdad, Wright said.
At dawn, gunmen stormed the home of two families belonging to the influential Sunni Mashhada tribe, said police First Lieutenant Haider Satar. Two fathers and their four sons were separated from their wives and sisters, then executed at point-blank range.
In the morgue in nearby Mahmoudiya, news footage showed at least two victims had their hands bound behind their backs.
Also yesterday, the Al Qaeda- affiliated group Islamic State of Iraq posted an online video purporting to show the execution of 18 Iraqi security troops, shot in the back of their heads while kneeling in a field.
The three-minute video, posted on a website previously used by the Islamists, said the 18 kidnapped government security forces were slain in retaliation for the alleged rape of a Sunni woman by members of the Shi'ite-dominated police. The video's authenticity could not be verified.
The group also claimed responsibility for the deaths of 14 policemen whose bodies were found Friday in the northeast province of Diyala.
US forces, meanwhile, reported airstrikes and raids on what it called Sunni militant bases linked to Al Qaeda in Iraq.
Prime Minister Nouri al- Maliki, a Shi'ite, is under pressure from Washington to take a stronger hand against Sunni insurgents and the Shi'ite militia that forms part of his power base.
In an interview , he said he would reshuffle his 39-seat Cabinet soon and pursue criminal charges against political figures -- and even members of Parliament -- linked to extremists. He said there has been coordination between Iraqi and multinational forces from the beginning of the year "to determine who should be arrested and the reasons behind arresting them."
US officials had been urging Maliki to cut ties to anti-American Shi'ite cleric Moqtada al-Sadr and form a new alliance of mainstream Shi'ites, moderate Sunnis, and Kurds.