Both sides blame the other for the biggest outbreak in violence since a 1994 ceasefire.
Bachelet’s office said it had received reports that it had not yet been able to verify that some 53 civilians, including children, had been killed in the fighting since September 27.
Some 400 lives have so far been lost including military casualties, and thousands of people have fled their homes.
“I remind all parties to the conflict to uphold their obligations under international humanitarian law to protect civilians and civilian infrastructure,” Bachelet said.
All sides in the conflict have an obligation to avoid “the use of explosive weapons with wide area effects in populated areas,” she added.
Bachelet also appealed to countries “with influence over parties to the conflict … to do everything within their power to ensure respect for international humanitarian law, including the protection of civilians.” Bachelet voiced particular outrage over reports that cluster munitions had been used in the conflict area.
“Cluster munitions scatter small, often bright or colourful bomblets over wide areas, many of which fail to explode immediately but can then kill and maim for years afterwards,” she pointed out.
“The use of such munitions should stop immediately.” The UN rights chief also called on all sides to refrain from using “inflammatory, pejorative or discriminatory language to stoke divisions.”
“Hate speech leads nowhere but to a mutually dehumanising and destructive hatred that, as we tragically see now, periodically erupts into conflict and loss of life,” she said.
And she warned that the violence could hamper efforts to rein in the spread of Covid-19 in the region.