Syrian regime forces are raining death on Aleppo, killing hundreds of people in air strikes that were either "criminally" indiscriminate or "deliberately" aimed at civilians, a rights group said Saturday.

"Government forces have really been wreaking disaster on Aleppo in the last month, killing men, women, and children alike," said Ole Solvang, senior emergencies researcher at Human Rights Watch.

"The Syrian Air Force is either criminally incompetent, doesn't care whether it kills scores of civilians -- or deliberately targets civilian areas," Solvang added.

The HRW statement comes six days after the launch of a massive aerial campaign against opposition-held areas of Aleppo, once Syria's commercial capital, involving dozens of warplane strikes and helicopter attacks using TNT-packed barrels.

The New York-based organisation cited the Syrian Network for Human Rights as saying 232 civilians were killed from December 15 to 18.

HRW concluded that the attacks, which targeted both Aleppo city and its province, showed "government forces had used means and methods of warfare that... could not distinguish between civilians and combatants, making attacks indiscriminate and therefore unlawful".

The group also condemned the reported use of the highly destructive so-called barrel bombs.

HRW "believes that military commanders should not, as a matter of policy, order the use of explosive weapons with wide-area effects in populated areas due to the foreseeable harm to civilians," it said.

HRW also lashed out against rebels for firing rockets and mortar rounds into civilian areas in government-controlled parts of Aleppo.

The city has been split into rebel and regime-controlled areas since mid-summer last year, when rebels launched a massive offensive to try to take Syria's second city.

Ever since, Aleppo has suffered daily violence.

In the latest escalation of fighting, even schools were targeted, said HRW.

The statement cites a field doctor as saying at least 14 civilians, including two teachers, four children and one woman, were killed in an explosion at a school in rebel-held east of Aleppo.

"When I reached the Taiba school I saw that a rocket had struck just outside the gate of the school. Several people who were standing next to the gate were killed," HRW cited the doctor as saying.

"One 11-year-old boy, our neighbour, had been cut into three pieces. I also saw the guard and three or four teachers who were killed."