Monday's suicide bombing , which killed 22 people and injured more than 100, many of them young people, took place just after Grande had finished performing. She later cancelled several concerts scheduled in London and Europe through June 5.
"I'll be returning to the incredibly brave city of Manchester to spend time with my fans and to have a benefit concert in honor of and to raise money for the victims and their families. ... I will have details to share with you as soon as everything is confirmed," Grande wrote.
In her Instagram posting, she said that her "Dangerous Woman" concert tour was intended to be a "space for my fans, a place for them to escape, to celebrate, to heal, to feel safe and to be themselves."
She said the victims would be "on my mind and in my heart everyday ... for the rest of my life."
But she added defiantly: "We will not quit or operate in fear. We won't let this divide us. We won't let hate win."
Gallagher tweeted that he was "in total shock and absolutely devastated" by the attack.