The report by the London-based rights group said Syrian forces were engaging in a scorched-earth policy in some areas, killing some civilians and torturing others, shooting livestock and burning crops and houses in rebel-held areas.
Amnesty said the attacks appeared to increase as the 15-month uprising has transformed into an armed conflict between rebels and Syrian forces.
The group said it based its information on more than 200 interviews with residents in 23 Syrian towns and villages over six weeks, starting in mid-April.
Amnesty said it also documented incidents of rebels kidnapping and killing captured soldiers and pro-government thugs, known as "shabiha," but said the vast majority of abuses were committed by government forces and their allies.
"The frequency and brutality of government reprisals against towns and villages supportive of the opposition has escalated, in an apparent bid to punish the inhabitants ... and to frighten them into submission," the report said.
"The scale of the attacks, and the manner in which they were carried out, indicates that such crimes were perpetrated as part of a deliberate policy," it said.
In one incident, an Amnesty researcher saw Syrian security forces and their loyalist militias opening fire on demonstrators and passers-by, including children, to quell a protest in the northern city of Aleppo.
It was one of the few that Amnesty itself witnessed. The testimonies it gathered could not be independently confirmed. The Syrian government had no comment on the report.
The group said it received the names of more than 10,000 people killed in the fighting.
Amnesty said residents told them of a system of reprisal raids by Syrian armed forces and their militias, often in the wake of attacks by rebels. They said the forces would sweep into town in tanks and armored vehicles, sometimes backed up by helicopters, firing indiscriminately. After entering, soldiers and shabiha would go door to door looking for wanted people, or simply to terrorize residents, the report said.
One woman said she found the charred remains of her elderly husband mixed with the ashes of her burned-down home. Residents said their neighbor was shot and wounded, and then dragged into a building that was set on fire, leaving him to burn to death.
Other residents were shot out while fleeing town. The attacks often appeared punitive—the father, brother or neighbor of a wanted man was killed.
Among the dozens of incidents recorded in the report was the case of Safwan Qaraush, 45, a father of five who suffered progressively worse psychiatric illnesses. He was found shot on the head in late March, still clutching his blanket over his head, "as if he had been afraid when he was shot," said a relative in the town of Sarmin. Amnesty did not give the relative's name, saying many feared they, too, would be punished.
In the city of Taftanaz, more than 20 men of the Ghazal family were killed between April 3 and 4, Amnesty said. Their relatives said 16 of the men, some of whom were rebel fighters, were taken from a basement where they were sheltering with their families. Their bullet-riddled bodies were found scattered near the basement. The others, including Ghassan Ghazal, 75, were killed in separate attacks targeting the family.
Amnesty said some incidents could be considered "crimes against humanity and war crimes."
The rights group called on the international community to do more to halt the violence, saying a lack of real pressure on the regime was allowing it to act "with utter impunity." The group said an arms embargo was needed, as was beefing up the mission of U.N. observers in Syria to ensure they could better investigate abuses.
"Such inaction by the international community ultimately encourages further abuses," said researcher Donatella Rovera.
Amnesty called on Russia and China to halt weapons transfers to Syria. Russia denies its weapons are being used to crack down on Syrian activists.