Noisy demonstrators disrupted shopping at suburban malls and marched through a district of bars and restaurants on Saturday, but the protests were peaceful following sporadic vandalism and violence a night earlier.
"We have also been informed that local crowd security personnel would not be at full capacity", they explained.
The protests followed raucous marches in downtown St Louis on Friday and through the city's posh Central West End area during the night.
Authorities say four of the nine people arrested overnight during protests in the St. Louis suburb of University City will face felony destruction of property charges.
The Irish band were booked to play at The Dome at America's Center on Saturday night, while English singer Sheeran had sold-out a Sunday night show at the Scottrade Center.More news: Girl, 12, stabbed friend 19 times 'to please' Slenderman
Promoter Live Nation and U2 wrote in a statement that the St. Louis Police Department would not be able to provide the "standard protection for our audience as would be expected for an event of this size" for the concert scheduled for Saturday 16 September.
Stockley had fired five shots at Smith, following a high speed police chase after he believed he witnessed the man engaging in a drug deal.
"In light of this information, we can not in good conscience risk our fans" safety by proceeding with tonight's concert. "Although we do so with regret, the cancellation is according to us the only acceptable outcome in the current environment".
Protesters said Sunday that the six-minute silence symbolizes the six years between the death of Anthony Lamar Smith and the acquittal of the white former police officer who was charged in the black suspect's shooting death.
Owing to a lack of adequate police protection at their performance venue following the city's protests of the Jason Stockley acquittal verdict, the band has made a decision to cancel this evening's concert. Prosecutors said the officer planted a gun in Smith's vehicle after the shooting. At least 10 officers were hurt and more than 20 people were arrested.