assume_role with region

[pritamrungta]

My AWS account setup has Service Control Policies that block access to all regions except us-east-2

I'm able to assume a role using CLI:
aws sts assume-role --role-arn ROLE_ARN --role-session-name ROLE_SESSION_NAME --region us-east-2

However, getting access denied with boto assume_role method:

sts = boto3.client('sts', region_name='us-east-2')
sts.assume_role(RoleArn=ROLE_ARN, RoleSessionName=ROLE_SESSION_NAME)

In both cases, I also have AWS_REGION set in my env. Also, used various other combinations, but nothing helps, and I'm almost blocked on this with no clue.

Please suggest, how I can make this work.