Serious violations of international laws amounting to war crimes were committed during the battle for Aleppo last year, a report to the UN has said.

Civilians caught up in the fighting between July and December 2016 were "increasingly left vulnerable to repeated violations by all sides", the report by the Independent International Commission of Inquiry on the Syrian Arab Republic said.

The use of chlorine bombs by Syrian forces, resulting in "civilian casualties, many of them children", was also detailed in the report.

The report, which described the battle war as "a stage of unrelenting violence", said: "the use of chlorine, regardless of the presence of a valid military objective, is prohibited by customary international humanitarian law."

It added: "The continued use of chlorine by Syrian forces evinces a blatant disregard for international legal obligations, and also amounts to the war crime of indiscriminate attacks against a civilian population."

The report also condemned "brutal" tactics used by pro-government forces, which it accused of deliberately starving civilians.

It said the siege "simultaneously deprived civilians of freedom of movement and prevented basic commodities, including food and medical supplies, from entering the city".

The "widely used" tactic of "surrender or starve" had "proven disastrous of civilians", the report said.

It concluded: "While the deprivation of supplies might have ultimately forced armed groups to surrender, the achievement of this result was accelerated by daily Syrian and Russian airstrikes, which claimed hundreds of lives and destroyed vital civilian infrastructure."

The 37-page report also accused Syrian forces of deliberately obstructing the delivery of humanitarian aid, while bombarding hospitals which had not military targets "in or around the vicinity".

It described an airstrike on a humanitarian aid convoy which killed 15 aid workers as "one of the most egregious".

"Syrian forces committed the war crimes of deliberately attacking humanitarian relief personnel, denial of humanitarian aid, and attacking civilians," said the report.

It added that the same hospitals were "repeatedly bombarded" within two specific time frames, which "strongly suggests that pro government forces committed the war crimes of intentionally targeting protected objects, medical personnel and transport."