Syria's air force has repeatedly carried out "indiscriminate, and in some cases deliberate" airstrikes against civilians, Human Rights Watch said in a new report.
The attacks are serious violations of international humanitarian law, and those who commit such violations with criminal intent are responsible for war crimes, the rights group said.
The claims are laid out in an 80-page report titled "Death from the Skies," based on visits to 50 sites of government airstrikes in opposition-controlled areas in Aleppo, Idlib and Latakia provinces.
The group's researchers carried out more than 140 interviews with witnesses and victims.
"In village after village, we found a civilian population terrified by their country's own air force," said Ole Solvang, a researcher for the rights group, who visited the sites and conducted many of the interviews.
"These illegal airstrikes killed and injured many civilians and sowed a path of destruction, fear and displacement."
Human Rights Watch said bakeries and hospitals have been targeted, in violation of the laws of war.
But Sharif Shahadeh, a lawmaker in the Syrian parliament, questioned the accuracy of the Human Rights Watch report.
No military target, group says
For the report, Human Rights Watch documented in detail eight airstrikes on four bakeries.
Its research "indicates government forces targeted bakeries and civilians waiting in breadlines in airstrikes as well as in artillery attacks," the group said.
"For each of these attacks, Human Rights Watch was not able to identify any military target, such as fighters or weapons, in the vicinity."
It cites the Syrian Revolution General Commission, a local opposition group, as saying Syrian forces have attacked 78 bakeries across Syria, either by airstrikes or artillery shelling.
Repeated airstrikes on two hospitals in the areas Human Rights Watch visited "strongly suggest that the government also deliberately targeted these facilities."
The rights group accuses the Syrian armed forces of using means such as unguided bombs, and methods such as fighter jets and high-flying helicopters, "that under the circumstances could not distinguish between civilians and combatants, and thus were indiscriminate."
Altogether, the airstrikes documented by Human Rights Watch killed at least 152 civilians, though the actual number is probably higher.
According to a network of local Syrian activists, airstrikes have killed more than 4,300 civilians across Syria since July 2012, the rights group said.
CNN is unable to independently confirm reports of casualties in Syria because access by international media is heavily restricted.
Shahadeh, the pro-government lawmaker, told CNN Arabic that the information available to lawmakers, based on intelligence reports, indicates "that the Syrian military air force only strike the locations of the terrorist armed groups," the term the government uses for rebel forces.
"For months, the majority of the reports issued by international organizations and some even by the United Nations include blatant political accusations rather than factual or technical investigations.
"There is no benefit for the regime to target civilians who are already suffering from the criminal acts carried out by the terrorist organizations that the regime troops are fighting."
The Syrian government has accused rights group of misrepresenting the facts and favoring the "terrorist groups" it says are behind the violence in Syria.
Human Rights Watch points out that the obligation to minimize harm to civilians applies to all parties to a conflict and that the rebels are not blameless.
"The Free Syrian Army (FSA) and other Syrian armed opposition groups did not take all feasible measures to avoid deploying forces and structures such as headquarters in or near densely populated areas," the report said.