ISTANBUL -- After a week without bread, people in the small central Syrian town of Halfaya got word two days before Christmas that a shipment of flour had arrived at the main bakery, prompting several hundred to queue up for the staple of life in the war-ravaged land.

For the Syrian air force, it was a moment of lethal opportunity. Soon, a Sukhoi-22 ground attack plane flew over the bakery and dropped eight bombs, each filled with cluster bomblets. The first struck 150 feet from the bakery, but the second was a direct hit on the bread line, killing at least 68 people, witnesses said.

“More than one bomb went off, and lots of smaller explosions. I couldn’t count the number, there were so many,” said Samer al Hamwi, a local activist. “I saw body parts from 200 meters. When I got closer, I saw people in front of the bakery all piled on top of each other. Blood and body parts were everywhere.”

The Halfaya massacre was only one of scores of artillery or air attacks on bread lines and bakeries last year, according to data McClatchy has compiled from multiple Syrian sources.

Two Syrian opposition groups say government forces have attacked bread lines and bakeries at least 100 times, causing hundreds of casualties and in most cases destroying the bakeries. A McClatchy investigation found another source for 80 of those attacks, either from videos posted on YouTube at the time of each attack or from subsequent interviews with eyewitnesses, activists and municipal council officials.

The attacks couldn’t have been inadvertent: At least 14 bakeries were targeted more than once, in some instances four or five times over months.

A spokesman for the U.N.’s high commissioner for human rights said the findings suggested a government strategy, and he called for an end to such attacks.

"The number of reported attacks on bakeries and bread lines is extraordinarily high and, if verified on anything like this scale, it would suggest that this cannot be accidental,” Rupert Colville told McClatchy. “If such attacks are indeed proved to be systematic or widespread targeting of civilian populations, then they may amount to both crimes against humanity and war crimes. All parties must halt all such attacks.”

The assaults on bakeries are a particularly perverse development in a war in which millions of people have been forced to flee their homes and face winter with inadequate shelter and dwindling food supplies. Rebel sympathizers say the attacks clearly are retaliation for rebel advances and that the government of President Bashar Assad is using his air force and artillery to punish civilians in rebel-held zones.

In Halfaya, the bread line bombing came two days after rebel forces attacked a government checkpoint, forcing government troops and allied Shabiha militia to abandon the town and its hospital.

The New York-based advocacy group Human Rights Watch first documented assaults on bread lines and bakeries in a report in August. The group said then that the Assad regime had targeted 10 bakeries in Aleppo, Syria’s commercial capital, killing and wounding scores of people. It said no fighting had been under way in any of the 10 cases and there was no significant presence of rebel fighters.

McClatchy’s review found that the attacks go far beyond that report, however. Since August, there have been more than 80 attacks, according to the two Syrian opposition groups: the Syrian Revolution General Commission, an umbrella for human rights groups, and the Al Jazeera Homs Channel, a group of so-called citizen journalists based in Homs that has no link to the Qatar-based international television network. Both have posted their broader conclusions on the Internet and provided specific details to McClatchy.