GENEVA: All sides fighting over the Syrian city of Aleppo may be committing war crimes through indiscriminate attacks in civilian areas, U.N. human rights spokeswoman Ravina Shamdasani told a regular U.N. briefing in Geneva on Tuesday.

Last week insurgents launched an offensive against government-held western Aleppo, more than a month into an operation by the army to retake the city's rebel-held eastern districts, which it had already put under siege.

The U.N. estimates 250,000-275,000 civilians are trapped and 8,000 rebel fighters holed up in the eastern part.

"All parties in Aleppo are conducting hostilities that are resulting in large numbers of civilian casualties and creating an atmosphere of terror for those who continue to live in the city," Shamdasani said.

Over the weekend, the U.N. documented the deaths of more than 30 civilians, including 10 children, as well as dozens of injuries, resulting from strikes by mortars, rockets and other improvised explosive devices on western Aleppo, she said.

"The reported use of ground based missiles, along with the use of armed vehicles loaded with explosives, used in an area containing more than 1 million civilian inhabitants, is completely unacceptable and may constitute a war crime," Shamdasani said.

The high number of civilian casualties suggested the rebels were ignoring the "fundamental prohibition" on indiscriminate attacks and the principles of precaution and proportionality, she added.

The U.N. did not have detailed enough information to attribute the attacks to specific groups, she said.

Government forces and their allies were also continuing to shell opposition-held eastern Aleppo, and the U.N. had documented at least 12 civilian casualties, including two children, on Saturday and Sunday, she said.

"Strikes against hospitals, schools, market places, water facilities and bakeries are now commonplace and if proven to be intentional may amount to war crimes."