Barrel bombs — containers packed with explosives and projectiles that are dropped from helicopters — killed some 3,000 civilians in the northern Aleppo governorate last year, and have killed more than 11,000 in Syria since 2012, Amnesty said.
“I saw children without heads, body parts everywhere... it was how I imagine hell to be,” one factory worker told Amnesty.
Another resident said the streets had been filled with blood and described Syria’s second city as “the circle of hell”.
Rights groups have long raised concerns about barrel bombs, and the UN Security Council adopted a resolution early last year condemning their use in populated areas, vowing “further steps” in the case of non-compliance.
Syrian president Bashar al-Assad said in February that the Syrian air force did not use barrel bombs. US and European officials have said the denial is not credible.
Aleppo, near the Turkish border, is a major frontline in the Syrian war.
Syria’s four-year-old civil war began in 2011 when a government crackdown on a pro-democracy movement led to an armed uprising. Islamic State militants have taken advantage of the chaos to declare a caliphate in a swathe of Syria and Iraq.
The conflict has killed more than 220,000 people in Syria and uprooted some 7.6 million within the country. Nearly 4m have fled to nearby countries.
Government attacks using barrel bombs and other imprecise explosive weapons have targeted heavily-populated residential areas, including markets, transport hubs, mosques, hospitals, medical centres, and schools, according to Amnesty.
Armed opposition groups have also committed war crimes by using imprecise weapons such as mortars and improvised rockets fitted with gas canisters called ‘hell cannons’ in attacks that killed at least 600 civilians in 2014, the rights group said. It added that torture, arbitrary detention, and abduction of civilians in Aleppo by both sides was widespread.
Attacks from government and rebel forces have left civilians in Aleppo living in dire conditions, lacking basic supplies including food, medicine, water and electricity, and have hampered efforts to provide humanitarian aid.
“The international community has turned its back on Aleppo’s civilians in a cold-hearted display of indifference to an escalating human tragedy,” said Amnesty’s Middle East and North Africa program director Philip Luther.
The Syrian conflict should be referred to the International Criminal Court to bring the perpetrators to justice and help “stem the spiral of abuses”, he added.