“These are civilian objects, and it seems highly unlikely, given the persistent pattern of such attacks, that they are all being hit by accident,” Bachelet said, adding that the rising toll had been met with “apparent international indifference”.
The government began its offensive against the rebel enclave in northwest Syria, the last area of active insurgent opposition to President Bashar al-Assad, at the end of April, saying it was responding to violations of a truce.
Idlib and surrounding areas of the northwest were included in a “de-escalation” deal last year between Assad’s main ally Russia and Turkey, which backs some rebel groups, to reduce warfare and bombardment.
Over the past three months, the offensive has driven hundreds of thousands of people from their homes or temporary shelters to seek refuge near the border with Turkey and has killed hundreds of civilians, according to war monitoring groups.
Both the Syrian government and its Russian ally, whose air power has been critical to Damascus’ military gains in recent years, deny targeting civilians or civilian infrastructure.
The spike in violence has killed more than 740 civilians, according to the Syrian Observatory for Human Rights.
Aid groups have described the latest bloody episode of the civil war as a “nightmare”.
More than 400,000 people have fled violence in the area since the end of April, said David Swanson of the United Nations’ humanitarian coordination office OCHA.
He spoke as regime air raids pummelled a market in the Idlib province town of Saraqib, according to the Observatory.
The Britain-based monitor said one civilian was killed and several others were wounded there on Friday, four days after a similar attack killed more than seven.
It said two other civilians were killed and 20 others were wounded in regime attacks elsewhere in the region.
A photographer in Saraqib saw broken styrofoam crates, fruits and vegetables scattered on the dusty concrete floor near wrecked vegetable trucks.
“The al-Hal market is one of the main commercial hubs of the town,” Layth al-Abdullah, a rescue worker in the town, said.
He added the regime had shown “barbarity… in its killing of civilians and the destruction of their property.”
For her part, Bachelet said: “Intentional attacks against civilians are war crimes, and those who have ordered them or carried them out are criminally responsible for their actions.”
The region under attack is home to some three million people, nearly half of them already displaced from other parts of the country.
It covers nearly all of Idlib and parts of neighbouring Aleppo, Hama, and Latakia provinces.