Jomana Abedi, 18, told the Wall Street Journal that her brother was "kind" and "loving" and was surprised he carried out the attack which killed 22 people and injured over 50.
Jomana said she thinks her brother was driven by "revenge".
“I think he saw children - Muslim children - dying everywhere, and wanted revenge," she said.
“He saw the explosives America drops on children in Syria, and he wanted to revenge. Whether he got that is between him and God.”
Her comments have been slammed by Manchester residents, with Mark Session telling The Mirror: "There is no justification for the taking of a child's lives.
"It is sick to justify the arena bombing in such a way. It is abhorrent in fact. There is no place for her comments."
A family friend has said that Abedi's attack was the 23-year-old seeking revenge for the murder of his friend in 2016.
Abdul Wahab Hafidah, of Libyan descent, reportedly died after he was run down by a car and then stabbed in Manchester.
“I remember Salman at his funeral vowing revenge,” the friend said.
This article first published on Who.