EC2 Deregister Image Client.UnauthorizedOperation Error

Hi AWS,

I have whitelisted the IAM permission ec2:DeregisterImage in the SCP. I have tried to deregister the image both using console and AWS CLI. I am assuming an IAM role for doing this. I was following this Stackoverflow link https://stackoverflow.com/questions/41157866/cannot-deregister-ami-from-aws-an-error-occurred-attempting-to-deregister-amis to resolve the issue but none of the way worked out for me.

Please help.

Thanks