WASHINGTON (AFP) - US Secretary of State John Kerry Tuesday hit out the "brutality" of the Syrian regime of President Bashar al-Assad for its sustained barrel bomb campaign.

"Each and every day that the barrel-bombing of Aleppo continues, the Assad regime reminds the world of its true colors," Mr Kerry wrote in a statement.

"It is the latest barbaric act of a regime that has committed organized, wholesale torture, used chemical weapons, and is starving whole communities by blocking delivery of food to Syrian civilians in urgent need." More than 150 people have been killed in Syria's onetime economic hub and second city over the past four days, in a string of barrel bomb raids and other air strikes, the Syrian Observatory for Human Rights said.

At least eight people, including five children, were the latest victims killed on Tuesday when Syrian army helicopters unleashed a new wave of the bombs which Mr Kerry said were "filled with metal shrapnel and fuel." The bombs hit a mosque, which the Aleppo media center said was being used as a school.

"Given this horrific legacy, the Syrian people would never accept as legitimate a government including Assad," Mr Kerry said, referring to peace talks due to resume in Geneva next week aimed at installing a transitional government in the war-torn country.

"While the opposition and the international community are focused on ending the war... the regime is single-mindedly focused on inflicting further destruction to strengthen its hand on the battlefield and undermining hopes for the success of the Geneva II process," Mr Kerry said.

Aleppo has been divided since the rebels captured large swathes of the city in an offensive in the summer of 2012.